Pronunciation: (on'tOO, ôn'-; unstressed on'tu, ôn'-), [key]
1. to a place or position on; upon; on: to get onto a horse.
2. Informal.in or into a state of awareness about: I'm onto your scheme.
Also,surjective. Math.pertaining to a function or map from one set to another set, the range of which is the entire second set.
a combining form meaning “being,” used in the formation of compound words: ontogeny.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.