onto vs. one-to-one

preposition

  1. to a place or position on; upon; on.

    to get onto a horse.

  2. Informal.,  in or into a state of awareness about.

    I'm onto your scheme.

adjective

  1. Mathematics.,  Also pertaining to a function or map from one set to another set, the range of which is the entire second set.

adjective

  1. Also (of the relationship between two or more groups of things) corresponding element by element.

  2. one-on-one.