late 14c., from Latin sipho (genitive siphonis) "a siphon," from Greek siphon "pipe, tube for drawing wine from a cask," of unknown origin. Related: Siphonal.
1859, from siphon (n.). Figurative sense of "to draw off, divert" is recorded from 1940. Related: Siphoned; siphoning.
siphon gas into the tank