dol·phin 
(dŏlfĭn, dôl-)
(dŏlfĭn, dôl-)n. pl. dolphin or dol·phins
1.
a. Any of various marine toothed whales of the family Delphinidae, having a beaklike snout, a curved dorsal fin, and a slender streamlined body.
b. Any of several toothed whales inhabiting rivers and estuaries in South America and South Asia, having a long narrow beak, broad flippers, a flexible neck, and usually a reduced dorsal fin. A species native to the Yangtze River is thought to be extinct. Also called river dolphin.
2.
a. See dolphinfish.
b. See pompano dolphinfish.
3.
a. A buoy, pile, or group of piles used for mooring boats.
b. A group of piles used as a fender, as at a dock or around a bridge pier.
[Middle English, from Old French daulfin, blend of daufin and Old Provençal dalfin, both from Medieval Latin *dalfinus, from Latin delphīnus, from Greek delphīs, delphīn-, from delphus, womb (from its shape).]
dolphinbottlenose dolphin
Tursiops truncatus