starfish

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

• noun Any of various marine echinoderms of the class Asteroidea, characteristically having a thick, often spiny body with five arms extending from a central disk.

from The Century Dictionary.

• noun An echinoderm with five or more arms radiating from a central disk: applied to all the members of the Asteroidea and Ophiuroidea (see these words).
• noun The butter-fish or dollar-fish.
• noun In heraldry, a bearing representing a five-pointed star, the rays surrounded by short waving flames or the like, and having a small circle in the center.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) Any one of numerous species of echinoderms belonging to the class Asterioidea, in which the body is star-shaped and usually has five rays, though the number of rays varies from five to forty or more. The rays are often long, but are sometimes so short as to appear only as angles to the disklike body. Called also sea star, five-finger, and stellerid.
• noun (Zoöl.) The dollar fish, or butterfish.

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

• noun Any of various asteroids or other echinoderms (not in fact fish) with usually five arms, many of which eat bivalves or corals by everting their stomach.
• noun vulgar, slang, usually in translations of Japanese pornography an anus. See also chocolate starfish.
• noun obsolete Any many-armed or tentacled sea invertebrate, whether cnidarian, echinoderm, or cephalopod.

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

• noun echinoderms characterized by five arms extending from a central disk