From The Collaborative International Dictionary of English v.0.48:
Developer \De*vel"op*er\, n.
1. One who, or that which, develops.
[1913 Webster]
2. (Photog.) A chemical bath or reagent used in developing
photographs.
Note: By the action of the developer, the latent image on a
photographic plate or film, not perceptible to the eye
after exposure in the camera, is developed and becomes
visible.
[1913 Webster +PJC]
3. (Dyeing) A reagent used to produce an ingrain color by its
action upon some substance on the fiber.
[Webster 1913 Suppl.]
4. a corporation or individual who finances or organizes a
real estate development[5].
[PJC]