Definition of dolphin
1 a
:any of various small marine toothed whales (family Delphinidae) with the snout more or less elongated into a beak and the neck vertebrae partially fused
Note:
While not closely related, dolphins and porpoises share a physical resemblance that often leads to misidentification. Dolphins typically have cone-shaped teeth, curved dorsal fins, and elongated beaks with large mouths, while porpoises have flat, spade-shaped teeth, triangular dorsal fins, and shortened beaks with smaller mouths.
b
:any of several related chiefly freshwater toothed whales (as of the families Platanistidae and Iniidae) :river dolphin
2
:dolphinfish
4
:a spar or buoy for mooring boats;
also
:a cluster of closely driven piles used as a fender for a dock or as a mooring or guide for boats
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