OXFORD DICTIONARY
dolphin, n.
1 any of various porpoise-like sea mammals of the family Delphinidae having a slender beaklike snout.
2 (in general use) = DORADO 1.
3 a bollard, pile, or buoy for mooring.
4 a structure for protecting the pier of a bridge.
5 a curved fish in heraldry, sculpture, etc.
ME, also delphin f. L delphinus f. Gk delphis -inos
THESAURUS
dolphin
Chiroptera, Lagomorpha, Loch Ness monster, Primates, Rodentia, alevin, benthon, benthos, cetacean, fingerling, fish, fry, game fish, grilse, kipper, man-eater, man-eating shark, marine animal, minnow, minny, nekton, panfish, plankton, porpoise, salmon, sea monster, sea pig, sea serpent, sea snake, shark, smolt, sponge, tropical fish, whale
ROGET THESAURUS
dolphin
Ocean
N
sea, ocean, main, deep, brine, salt water, waves, billows, high seas, offing, great waters, watery waste, vasty deep, wave, tide, hydrography, hydrographer, Neptune, Poseidon, Thetis, Triton, Naiad, Nereid, sea nymph, Siren, trident,
dolphin, oceanic, marine, maritime, pelagic, pelagian, seagoing, hydrographic, bathybic, cotidal, at sea, on sea, afloat.