Definition of "onto" in English

preposition

1. Arriving upon or on top of (speaking of a physical or metaphorical movement).

   • My cat just jumped onto the keyboard.
   • A new drug has just come onto the market.

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.

adjective

1. (mathematics, of a function) Attaining each of the values in its codomain; having its image equal to its codomain.

   • Considered as a function on the real numbers, the exponential function is not onto, as it never takes on values less than or equal to zero.