I. ˈȯn-(ˌ)tü, ˈän- preposition
Date: 1581
1. : to a position on
2. : in or into a state of awareness about
put me onto your methods
3. — used as a function word to indicate a set each element of which is the image of at least one element of another set
a function mapping the set S onto the set T
II. adjective
Date: 1942
: mapping elements in such a way that every element in one set is the image of at least one element in another set
a function that is one-to-one and onto