combination (n.)

late 14c., combinacyoun, "act of uniting (two things) in a whole; state of being so united," from Old French combination (14c., Modern French combinaison), from Late Latin combinationem (nominative combinatio) "a joining two by two," noun of action from past participle stem of combinare "to unite, yoke together," from Latin com "with, together" (see com-) + bini "two by two," adverb from bi- "twice" (from PIE root *dwo- "two").

Sense of "a whole formed by uniting" is from 1530s; specific sense of "union or association of persons for the attainment of some common end" is from 1570s. Meaning "series of moves required to open a combination lock" is from 1880; combination lock, one requiring a certain combination of moves to open it, is from 1851. Related: Combinational.