(1):

(a.) Of or pertaining to a subsidy; constituting a subsidy; being a part of, or of the nature of, a subsidy; as, subsidiary payments to an ally.

(2):

(a.) Furnishing aid; assisting; auxiliary; helping; tributary; especially, aiding in an inferior position or capacity; as, a subsidiary stream.

(3):

(n.) One who, or that which, contributes aid or additional supplies; an assistant; an auxiliary.