(1):
(n.) The result of combining or uniting; union of persons or things; esp. a union or alliance of persons or states to effect some purpose; - usually in a bad sense.
(2):
(n.) The act or process of combining or uniting persons and things.
(3):
(n.) The act or process of uniting by chemical affinity, by which substances unite with each other in definite proportions by weight to form distinct compounds.
(4):
(n.) The different arrangements of a number of objects, as letters, into groups.