1. (mathematics, of a function) Assuming each of the values in its codomain; having its range equal to its codomain.
- Considered as a function on the real numbers, the exponential function is not onto.
1. Upon; on top of.
- My cat just jumped onto the keyboard.
2. (informal) Aware of.
- (The thought-police were onto my plans of World domination.)
3. (mathematics) Being an onto function with a codomain of (see below).
- The exponential function maps the set of real numbers onto the set of positive real numbers.