one-to-one

adjective

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

adjective

1. (of two or more things) corresponding exactly
2. denoting a relationship or encounter in which someone is involved with only one other personone-to-one tuition
3. maths characterized by or involving the pairing of each member of one set with only one member of another set, without remainder

noun

4. a conversation, encounter, or relationship between two people