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The name is originally from Greek δελφίς (delphís), "dolphin",[1] which was related to the Greek δελφύς (delphus), "womb".[2]The animal's name can therefore be interpreted as meaning "a 'fish' with a womb".[3] The name was transmitted via the Latindelphinus[4] (the romanization of the later Greek δελφῖνος – delphinos[5]), which in Medieval Latin became dolfinus and in Old French daulphin, which reintroduced the ph into the word. The term mereswine (that is, "sea pig") has also historically been used.[6]
The term 'dolphin' can be used to refer to, under the suborder odontoceti, all the species in the family delphinidae (marine dolphins including orcas and pilot whales) and the river dolphin superfamily Platanistoidea, which includes the families Iniidae(Amazon river dolphin), Lipotidae (Yangtze river dolphin) and Platanistidae (Ganges river dolphin and Indus river dolphin).[7][8]This term has often been misused in the US, mainly in the fishing industry, where all small cetaceans (dolphins and porpoises) are considered porpoises, while the fish dorado is called dolphin fish.[9] In common usage the term 'whale' is used only for the larger species under cetaceans,[10] while the smaller ones with a beaked or longer nose are considered 'dolphins'.[11] The name 'dolphin' is used casually as a synonym for bottlenose dolphin, the most common and familiar species of dolphin.[12] Killer Whales also belong to the delphinidae family and therefore qualify as dolphins. Though the terms 'dolphin' and 'porpoise' are used interchangeably, porpoises are not considered dolphins and have different physical features such as a shorter beak and spade-shaped teeth; they even differ in their behavior. Porpoises belong to the family Phocoenidae and share a common ancestry with the delphinidae under the suborder odontocetes.[12]
A group of dolphins is called a "school" or a "pod". Male dolphins are called "bulls", females "cows" and young dolphins are called "calves".[13]