showing movement to a position on the surface of or in contact with something
The cat leaped onto the windowsill to watch the birds outside.
The waiter carefully placed the tray onto the table without spilling a drop.
✦ from on + to, first appearing as one word in the 18th century
(mathematics) describing a function that maps every element of its codomain to at least one element of its domain; surjective
In the graph on the board, the professor showed that function f is onto.
A surjective or onto mapping hits every point in the codomain.
✦ specialized use of the common preposition in 1930s mathematical literature as a synonym for "surjective"
