a suffix occurring in words borrowed from French and other Romance languages (bassoon; balloon; dragoon; pontoon), and on this model occasionally used in the formation of new nouns in English (spittoon).
A Long List of Affixes: Suffixes, Prefixes, and Combining FormsSuffixes -able, -ible, -ile: (form adjs) able to, fit to, worthy, capable; apt to; subject to being ~-ed -ac: one affect with -ac, -al, -ane, -ar, -ary, -ch, -ese, -ic, -ical, -id, -ile, -ine, -ish, -ory: like, of, pertaining to; characterized by -aceae: families of plants -aceous, -ous: resemblance to a substance; full of -acy, -age, -ance, -ancy, -asm, -dom, -ence, -ency, -hood, -ism, -ity, -ment, -mony, -ness, -ry, -ship, …
Origin of -oon
as an English formative (e.g., in spittoon), extracted from words of various origins (buffoon, lagoon, etc.) but representing chiefly French -on in words stressed on the final syllable; compare Spanish -on, Italian -one, Latin -ōn-
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
spelling conventional in 15c.-17c. English to add emphasis to borrowed French nouns ending in stressed -on; also used to represent Italian -one, Spanish ón; all from Latin -onem. Used in rare cases to form English words, e.g. spittoon, octaroon.
Online Etymology Dictionary, © 2010 Douglas Harper