What’s the Plural of Locus: Understanding Grammatical Number in Biology

  • The word “locus” comes from Latin and denotes a specific location or point.
  • Its plural form is “loci,” following a common pattern in words with Latin roots.
  • Proper pronunciation and knowledge of its origin contribute to precision in communication.

The plural form of “locus” is “loci” (pronounced ‘loh-sigh’ or ‘loh-kee’). This transformation from singular to plural is common for words that have been adopted from Latin into English. Knowing both forms of the word allows for clearer communication, especially in academic and professional contexts where precision is paramount. Exploring the origin of “locus” further enhances understanding, providing insight into how its meaning has been shaped over time.

What’s the Plural of “Locus”?

A locus is a specific point or position, often used in contexts such as mathematics, science, and academia.

Singular to Plural Transformation

The transformation from singular to plural form for Latin-derived words often involves changing an ending of -us to -i. Here is how “locus” fits into this rule:


Usage in Sentences

Using “locus” and “loci” correctly in sentences helps to clarify their meaning and proper pluralization:

  • Singular: The scientists discovered a new locus for gene expression.
  • Plural: Researchers identified several loci responsible for the trait.

Mathematical and Scientific Contexts

In disciplines such as mathematics and genetics, the term takes on precise meanings:

  • Mathematics: Refers to a set of points satisfying certain conditions.
  • Genetics: Denotes the specific location of a gene or a sequence on a chromosome.

Loci are fundamental in discussions where precision is vital, and using the correct plural form emphasizes the accuracy and seriousness of the subject matter.

Common Mistakes

It’s not uncommon for people to mistakenly use “locuses” instead of “loci.” Below is a comparison to reinforce the correct usage:

  • Incorrect: The various locuses of activity in the brain can be mapped.
  • Correct: The various loci of activity in the brain can be mapped.
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What’s the Singular of “Locus”?

Latin OriginEnglish Usage
singular: locusRefers to a single point or place

In sentences, the singular form “locus” is often used to indicate the central or primary place of a particular activity or situation. For instance:

  • The locus of the conference is the main auditorium.
  • Our research has identified the gene’s locus on the chromosome.


To ensure clarity when teaching or using the term “locus,” here are important points:

  • “Locus” is the singular term for a specific location or center of activity.
  • It is pronounced /ˈləʊkəs/ in the Received Pronunciation and /ˈloʊkəs/ in General American.
  • The plural form, “loci,” is used when referencing multiple locations or centers of activities.

Defining the Word “Locus”

The term locus is derived from Latin, referring to a specific location or place. In English, “locus” (pronounced /ˈloʊ.kəs/) serves a similar function, indicating the exact position where something occurs or is situated. Therefore, the primary meaning of locus is centered on the aspect of geographic or abstract positioning. Below are foundational characteristics of the term:

  • Etymology: From Latin, meaning place or location.
  • Usage: Commonly used in scientific contexts, such as mathematics and genetics, as well as in more general language.
ContextExample Sentence
MathematicsThe locus of points equidistant from a single point forms a circle.
GeneticsA gene is located at a specific locus on a chromosome.

In more general usage, locus can act metaphorically to refer to a central area of activity or the main site for an event, not necessarily limited to a physical space. In terms of grammar, locus functions as a noun.

General UsageExample Sentence
MetaphoricalThe town square was the locus of the festival activities.

In linguistics, specifically within the realm of plurality, certain nouns have unique plural forms often adhering to their original language’s rules. For locus, the plural form is “loci” (pronounced /ˈloʊ.saɪ/ or /ˈloʊ.kaɪ/), adhering to this pattern of Latin-derived nouns:

  • Singular: locus
  • Plural: loci
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Other Latin Nouns

In Latin, nouns are known to have various endings, which can change depending on their case (nominative, accusative, etc.) and number (singular or plural). Understanding the plural forms of Latin nouns is crucial for grasping the language’s structure and making accurate translations.

First Declension
Generally, Latin nouns in the first declension are feminine and feature an -ae ending in the nominative plural. For instance:

  • Singular: puella (girl)
  • Plural: puellae (girls)

Second Declension
Nouns in the second declension can be masculine or neuter and usually end in -i for the masculine nominative plural and -a for the neuter nominative plural. Consider these examples:

Masculine Neuter
(master, lord) (war)
(masters, lords) (wars)

Third Declension
The third declension encompasses a mix of genders and typically ends in -es for the plural. For example:

  • Singular: rex (king)
  • Plural: reges (kings)

Fourth Declension
Fourth declension nouns often have an -us ending in the singular form and -us in the plural in the nominative case:

  • Singular: fructus (fruit)
  • Plural: fructūs (fruits)

Fifth Declension
Fifth declension nouns are mostly feminine, ending with -es in the plural nominative:

  • Singular: res (thing, matter)
  • Plural: rēs (things, matters)

Here’s a quick reference for the common plural endings across declensions:

  • First Declension: -ae
  • Second Declension (Masculine): -i
  • Second Declension (Neuter): -a
  • Third Declension: -es
  • Fourth Declension: -ūs
  • Fifth Declension: -ēs

Examples of the Word “Locus” (Singular) Used in Sentences

The scientist identified the locus of the infection within the patient’s tissue.Illustrates “locus” referring to a specific location.
In mathematics, they were tasked to find the locus that represents all the possible positions of a point.Shows “locus” used in a technical, geometrical sense.
  • In genetics: “The gene responsible for eye color is found at a specific locus on chromosome 15.”
  • In psychology: “An individual with an internal locus of control believes they can influence events and their outcomes.”
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Examples of “Loci” (Plural) Used in Application

In the realms of psychology and mathematics, the term “loci” finds usage in distinct contexts. The plural form of “locus,” “loci” is integral to discussions relating to control perception and geometric locations. Here, we analyze how “loci” is applied within these fields.

Psychology Application
In personality psychology, “loci” refers to the positions or locations on the spectrum of locus of control. These are illustrative of how individuals perceive the control over the events in their lives.

Internal LociExternal Loci
DeterminationDivine Will

Individuals with an internal locus of control attribute outcomes to their own actions, while those with an external locus attribute events to external factors.

Mathematics Application
In geometry, “loci” denotes sets of points that conform to certain conditions.

  • The locus of points equidistant from a single point forms a circle.
  • Loci can be intricate curves or figures like parabolas and ellipses, each with its own defining mathematical properties.

Here are two key geometric loci:

Geometrical LociDescription
Straight LineA set of points equidistant from two given points forms a line segment.
Perpendicular BisectorThe locus of points equidistant from the endpoints of a line segment lies on a line that cuts the segment into two equal parts at a right angle.

Origin of the Word “Locus”

The term “locus” is deeply rooted in Latin, where it primarily denotes a “place” or “location.” This origin is critical to understanding the term’s development and application in various contexts, such as mathematics, genetics, and rhetoric. The adoption of “locus” into English usage is a testament to the language’s ability to assimilate and preserve the essence of words from different languages.

Latin OriginMeaning in Latin
locusPlace / Location

In the English language, “locus” retains much of its Latin essence, signifying a point or place where something occurs or is situated. From linguistics to biology, “locus” has found its niche, often being used to describe central points of interest or activity within a specific area.

  • Usage in Mathematics:

    • Point on a curve
    • Set of points satisfying particular conditions
  • Usage in Genetics:

    • Site on a chromosome where a particular gene or sequence of DNA is located

The plural form of “locus” is “loci,” which directly follows the standard rule for Latin-based nouns ending in ‘-us’ that typically take an ‘-i’ ending in the plural form.


The passage of “locus” into the realm of common English parlance exemplifies the broader narrative of linguistic evolution, where words and meanings are transported across time and tongues, ever adapting yet definitively anchored to their etymological origins.


  1. Definition of locus.
  2. Sentences using locus.
  3. Origin of locus.

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