aquanaut (n.)

word-forming element meaning "water," from Latin aqua "water; the sea; rain," cognate with Proto-Germanic *akhwo (source of Old English ea "river," Gothic ahua "river, waters," Old Norse Ægir, name of the sea-god, Old English ieg "island"), from PIE root *akwa- "water."

1824, "art of aerial navigation by means of a balloon," from aeronautic (1784), from French aéronautique, from aéro- (see aero-) + nautique "of ships," from Latin nauticus, from Greek nautikos "pertaining to sailing" (see nautical). Also see -ics. Aeronaut "balloonist" is from 1784, from French aéronaute.