receptor

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Physiology A specialized cell or group of nerve endings that responds to sensory stimuli.
• noun Biochemistry A molecular structure or site on the surface or interior of a cell that binds with substances such as hormones, antigens, drugs, or neurotransmitters.

from The Century Dictionary.

• noun A molecular complex of a cell through the union with which alien cell-products or cell-constituents can produce, their specific effects upon the coll. These same receptors, owing to the presence of which the cell is open to attack, when cast off from the cell constitute its most effective defenses. Also called side-chain. See immunity, 5.
• noun In wireless telegraphy, a receiver.
• noun The terminal expansion in skin or mucous membranes of a sensory nerve.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun biochemistry, medicine A protein on a cell wall that binds with specific molecules so that they can be absorbed into the cell in order to control certain functions.
• noun biology Any specialized cell or structure that responds to sensory stimuli.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a cellular structure that is postulated to exist in order to mediate between a chemical agent that acts on nervous tissue and the physiological response
• noun an organ having nerve endings (in the skin or viscera or eye or ear or nose or mouth) that respond to stimulation