Definition of “combination”

noun

1. the act of combining or state of being combined
2. a union of separate parts, qualities, etc
3. an alliance of people or parties; group having a common purpose
4. 1. the set of numbers that opens a combination lock
   2. the mechanism of this type of lock
5. British a motorcycle with a sidecar attached
6. mathematics 
   1. an arrangement of the numbers, terms, etc, of a set into specified groups without regard to order in the group  ⇒ the combinations of a, b, and c, taken two at a time, are ab, bc, ac 
   2. a group formed in this way. The number of combinations of a group formed in this way. The number of combinations of n  objects taken a group formed in this way. The number of combinations of objects taken r  at a time is a group formed in this way. The number of combinations of objects taken at a time is n !/[(a group formed in this way. The number of combinations of objects taken at a time is !/[(n  – a group formed in this way. The number of combinations of objects taken at a time is !/[( – r )!a group formed in this way. The number of combinations of objects taken at a time is !/[( – )!r !]. Symbol: a group formed in this way. The number of combinations of objects taken at a time is !/[( – )!!]. Symbol: _n Ca group formed in this way. The number of combinations of objects taken at a time is !/[( – )!!]. Symbol: C_r Compare permutation (sense 1)
7. the chemical reaction of two or more compounds, usually to form one other compound
8. chess a tactical manoeuvre involving a sequence of moves and more than one piece