When the word dolphin was first used in English in a fourteenth century romantic epic about Alexander the Great, it was spelled delfyn, and other spellings around that time included delphin, dalphyn, daulphin, dolphyn, dolfyn, dolphyne, and doulphyn; the modern form didn't really become widely used until the 1600s. Delfyn came from the Old French word daufin, which, through Medieval Latin dolfinus and Latin dolphinus (both with the same definition), traces to the Ancient Greek noun delphys, meaning "womb". Etymologists aren't really sure why that's the case, but theories include a perceived resemblance in shape or something to do with them giving birth. Delphys, which also evolved into the -delphia part of Philadelphia, eventually derives from the Proto-Indo-European reconstruction gwelb, also meaning "womb"
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.