mid-15c., Scottish ydy, possibly from Old Norse iða "whirlpool," from Proto-Germanic *ith- "a second time, again," which is related to the common Old English prefix ed- "again, backwards; repetition, turning" (forming such words as edðingung "reconciliation," edgift "restitution," edniwian "to renew, restore," edhwierfan "to retrace one's steps," edgeong "to become young again"). Cf. Old English edwielle "eddy, vortex, whirlpool." The prefix is cognate with Latin et, Old High German et-, Gothic iþ "and, but, however." Related: Eddies.
1810, from eddy (n.). Related: Eddied; eddying.
A current, as of water or air, moving in a direction that is different from that of the main current. Eddies generally involve circular motion; unstable patterns of eddies are often called turbulence. See also vortex.