Ful

US: (fŏŏl)

WordReference Random House Unabridged Dictionary of American English © 2025

Ful  (fŏŏl), n., pl. Fuls, (esp. collectively) Ful. 

1. Language Varieties Fulani.

-ful, 

1. Pronouns a suffix meaning "full of,'' "characterized by'' (shameful;
   beautiful;
   careful;
   thoughtful);
   "tending to,'' "able to'' (wakeful;
   harmful);
   "as much as will fill'' (spoonful).

• Middle English, Old English -full, -ful, representing 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.

WordReference Random House Learner's Dictionary of American English © 2025

-ful, suffix. 

1. Pronouns
   • -ful is attached to nouns to form adjectives with the meaning "full of;
     characterized by'':
     beauty + -ful → beautiful (= full of beauty);
     care + -ful → careful (= characterized by care).
   • -ful is attached to verbs to form adjectives with the meaning "tending to;
     able to'':
     harm + -ful → harmful (= tending to harm);
     wake + -ful→ wakeful (= tending to stay awake).
   • -ful is attached to nouns to form nouns with the meaning "as much as will fill'':
     spoon + -ful → spoonful (= as much as will fill a spoon);
     cup + -ful → cupful (= as much as will fill a cup).

Collins Concise English Dictionary © HarperCollins Publishers::

-ful suffix

1. (forming adjectives) full of or characterized by: painful, spiteful, restful
2. (forming adjectives) able or tending to: helpful, useful
3. (forming nouns) indicating as much as will fill the thing specified: mouthful, spoonful

Etymology: Old English -ful, -full, from full¹Where the amount held by a spoon, etc, is used as a rough unit of measurement, the correct form is spoonful, etc: take a spoonful of this medicine every day. Spoon full is used in a sentence such as he held out a spoon full of dark liquid, where full of describes the spoon. A plural form such as spoonfuls is preferred by many speakers and writers to spoonsful