/on"tooh, awn"-/ ; unstressed /on"teuh, awn"-/ , prep.
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.
adj.
3. Also, surjective . Math. pertaining to a function or map from one set to another set, the range of which is the entire second set.
[ 1575-85; ON + TO ]