Dolphin
wiktionary
From Middle English dolfin, from Old French daulphin, dalphin, daufin, from Latin delphīnus, from Ancient Greek δελφίς(delphís), from δελφύς(delphús, “womb”). Compare Swedish delfin. Doublet of dauphin. Displaced native mereswine(“dolphin or porpoise”), from Old English mereswīn(literally “sea pig”).
Ultimately from 3rd Duke of Alba ( duc-d'Albe in French), who was the first to build this type of structure in the Spanish Netherlands in the 16th century. Possibly from Dutch dukdalf, or the plural dukdalven, through elision of the initial duk-.
etymonline
dolphin (n.)
popular name of a diverse group of marine mammals, also including the porpoise (but the true dolphin has a longer and more slender snout), mid-14c., dolfin, from Old French daulphin, from Medieval Latin dolfinus, from Latin delphinus "dolphin," from Greek delphis (genitive delphinos) "dolphin," related to delphys "womb," perhaps via notion of the animal bearing live young, or from its shape. Popularly applied to the dorado from late 16c. through some confusion. The constellation is so called from early 15c.
