a suffix meaning "full of," "characterized by" ( shameful; beautiful; careful; thoughtful ); "tending to," "able to" ( wakeful; harmful ); "as much as will fill" ( spoonful ).
[ ME, OE -full, -ful, repr. full, ful FULL 1 ]
Usage . The plurals of nouns ending in -FUL are usually formed by adding -s to the suffix: two cupfuls; two scant teaspoonfuls. Perhaps influenced by the phrase in which a noun is followed by the adjective FULL ( both arms full of packages ), some speakers and writers pluralize such nouns by adding -s before the suffix: two cupsful.