Probably from Old Norse 'iða' (whirlpool)—water that turns back against the main current.
A circular current of water or air running contrary to the main current, causing a small whirlpool.
Probably from Old Norse 'iða' (whirlpool) or Old English prefix 'ed-' (back, again), suggesting water that turns back on itself. The concept of a 'back-turning' current captures the essential nature of an eddy. Key roots: iða (Old Norse: "whirlpool").