- to a place or position on; upon; on: to get onto a horse.
- Informal. in or into a state of awareness about: I’m onto your scheme.
- Also surjective. Mathematics. 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.
- to a position that is onstep onto the train as it passes
- having become aware of (something illicit or secret)the police are onto us
- into contact withget onto the factory
- existence or beingontogeny; ontology
prep.1580s, as on to, from on + to. Appeared much later than parallel into. As a closed compound (on analogy of into), first recorded 1715. 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). pref.
- Organism; being:ontogeny.