a suffix meaning “full of,” “characterized by” (shameful; beautiful; careful; thoughtful); “tending to,” “able to” (wakeful; harmful); “as much as will fill” (spoonful).
Origin of -ful
Middle English, Old English -full, -ful, representing full, ful full1
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.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
(forming adjectives) full of or characterized bypainful; spiteful; restful
(forming adjectives) able or tending tohelpful; useful
(forming nouns) indicating as much as will fill the thing specifiedmouthful; spoonful
Word Origin for -ful
Old English -ful, -full, from full 1
Where 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
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
word-forming element meaning "full of, characterized by," Old English -full, -ful, suffix use of full (adj.).
Online Etymology Dictionary, © 2010 Douglas Harper