1. (mathematics) describing a relationship between two sets where each element of the first set is paired with exactly one element of the second set, and vice versa
   "A one-to-one mapping between names and ID numbers"
    
2. Directly between two individuals
   "one-to-one instruction";
   - one-on-one

1. A private meeting or conversation between two people
   "The manager scheduled a one-to-one with each team member";
   - one-on-one

Derived forms: one-to-ones

See also: matched, private

Encyclopedia: One-to-one