noun

1. a combining or being combined
2. a thing formed by combining
3. an association of persons, firms, political parties, etc. for a common purpose
4. 1. the series of numbers or letters used in opening a combination lock
   2. the mechanism operating such a lock
5. a one-piece undergarment combining an undershirt and drawers
6. Chem. a uniting of substances to form a compound
7. Math. any of the various groupings, or subsets, into which a number, or set, of units may be arranged without regard to order: dual combinations of A, B, C, and D are AB, AC, AD, BC, BD, CD
8. Pool a shot in which an object ball is pocketed as a result of being struck by another object ball
   in full combination shot

Etymology: ME combinacioun < LL combinatio, a joining two by two