2.16 Plurals of compound terms

(a) In forming the plurals of compound terms, pluralize the significant word. If both words are of equal significance, pluralize both. Pluralize the last one if no one word is significant in itself:

  • attorneys general
  • brigadier-generals
  • trade unions
  • judge advocates
  • orders-in-council
  • men drivers
  • women writers
  • assistant chiefs of staff
  • courts-martial
  • poets laureate

(b) When a noun is hyphenated with a preposition, the plural is formed on the noun:

  • fillers-in
  • hangers-on
  • passers-by
  • makers-up

(c) When neither word of a compound is a noun, the plural is formed on the last word:

  • also-rans
  • go-betweens
  • run-ins
  • higher-ups

(d) Add s to nouns ending in ful:

  • teaspoonfuls
  • cupfuls
  • handfuls
  • sackfuls