(1):

(n.) One that develops

(2):

(n.) A reagent used to produce an ingrain color by its action upon some substance on the fiber.

(3):

(n.) A chemical bath or reagent used in developing photographs.

(4):

(n.) A reagent by the action of which the latent image upon a photographic plate, after exposure in the camera, or otherwise, is developed and visible.

(5):

(n.) One who, or that which, develops.