a combining form meaning “being,” used in the formation of compound words: ontogeny.
Also especially before a vowel, ont-.
Origin of onto-
< New Latin < Greek ont- (stem of ón, neuter present participle of eînai to be) + -o- -o-
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
existence or beingontogeny; ontology
Word Origin for onto-
from Late Greek, from ōn (stem ont-) being, present participle of einai to be
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 "a being, individual; being, existence," from Greek onto-, from stem of on (genitive ontos) "being," neuter present participle of einai "to be" (see essence).
Online Etymology Dictionary, © 2010 Douglas Harper
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.