- a combining form meaning “nine, ninth,” used in the formation of compound words: nonagon.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
before a vowel non-
from Latin nōnus
Word Origin and History for nona-
before vowels non-, word-forming element from comb. form of Latin nonus "ninth" (see nones).
Online Etymology Dictionary, © 2010 Douglas Harper