noun one who, or that which, develops.
2. developer ·add. ·noun one that develops.
3. developer ·add. ·noun a chemical bath or reagent used in developing photographs.
4. developer ·add. ·noun a reagent used to produce an ingrain color by its action upon some substance on the fiber.
5. developer ·noun 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.