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 FULL1]
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.

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