Yours, Etc.: Origins and Uses of 8 Sign-Offs
"to make a moaning or murmuring sound," Old English swogan "to sound, roar, howl, rustle, whistle," from Proto-Germanic *swoganan (cf. Old Saxon swogan "to rustle," Gothic gaswogjan "to sigh"), from PIE imitative root *(s)wagh- (cf. Greek echo, Latin vagire "to cry, roar, sound"). The noun is late 14c., from the verb.