Compound nouns and their plurals

Filed in English Grammar

To change a singular compound noun into its plural form, we add –s to the principal word. With some compound nouns, -s is added to the first part.

Examples are given below.

Commander-in-chief (singular): commanders-in-chief (plural)
Father-in-law: fathers-in-law
Sister-in-law: sisters-in-law
Son-in-law: sons-in-law
Lady-in-waiting: ladies in waiting
Looker-on: lookers-on
Man-of-war: men-of-war
Hanger-on: hangers-on
Knight-errant: knights-errant

Some compound nouns form their plurals by adding –s to the last part.

Examples are given below.

Fountain pen: fountain-pens
Boy friend: boy friends
Maid-servant: maid-servants
Poet-laureate: poet-laureates
Step-son: step-sons
Assistant director: assistant directors
Lieutenant-governor: lieutenant governors

Names and their polite titles have the following plural forms:

Miss Smith (Singular): The Miss Smiths OR The Misses Smith (Plural)
Mr Brown (Singular): The Mr Browns OR The Messrs. Browns (Plural)
Mrs Robinson: The Mrs. Robinsons
Mr: Messrs

Foreign Plurals

Alumnus (singular): alumni (plural)
Analysis: analyses
Agendum: agenda
Appendix: appendices, appendixes
Focus: foci, focuses
Formula: formulae, formulas
Index: indices, indexes
Axis: axes
Basis: bases
Crisis: crises
Criterion: criteria
Curriculum: curricula
Datum: data
Ellipse: ellipses
Gymnasium: gymnasia
Terminus: termini, terminuses
Memorandum: memoranda
Phenomenon: phenomena
Radius: radii, radiuses
Syllabus: syllabi, syllabuses
Thesis: theses

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