Compound nouns form their plural by adding -s to the principal word:
sister-in-law | sisters-in-law |
vriting-table | vriting-tables |
editor-in-chief | editors-in-chief |
passer-by | passers-by |
In compounds with man/woman both words are pluralise:
man fiend | man friends |
journalist | journalists |
woman | woman |
woman doctor | women doctors |
Compounds ending in -man , change -man into -men in the plural. There is only a slight difference or none in the pronunciation.
policeman | policemen |
horseman | horsemen |
doorman | doormen |
postman | postmen |
Compounds ending in the -ful form their plural by adding -s:
handful | handfuls |
spoonful | spoonfuls |
cupful | cupfuls |
armful | armfuls |
Compounds containing no noun, form their plural by adding -s to the last word.
look-out | look-outs |
get-up | get-ups |
go-between | go-bettweens |
grown-up | grown-ups |