(1):

(n.) A substance added to an immunogenic agent to enhance the production of antibodies.

(2):

(a.) Helping; helpful; assisting.

(3):

(n.) An assistant.

(4):

(n.) A substance added to a formulation of a drug which enhances the effect of the active ingredient.

(5):

(n.) An ingredient, in a prescription, which aids or modifies the action of the principal ingredient.