whale shark

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

• noun A very large plankton-feeding shark (Rhincodon typus) of tropical and warm temperate waters, having a spotted body. It is the largest living fish, reaching a length of about 12 meters (39 feet).

from The Century Dictionary.

• noun A shark of the family Rhinodontidæ, Rhinodon typicus, one of the very largest sharks, and native of warm seas. See the technical names.
• noun The basking-shark (which see, with cut).

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

• noun A very large spotted shark, Rhincodon typus, of warm marine waters, similar to a whale, that feeds by filtering plankton from the water.

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

• noun large spotted shark of warm surface waters worldwide; resembles a whale and feeds chiefly on plankton