Is it ensure, insure, or assure?
also ox-bow, mid-14c., "wooden collar for an ox," from ox + bow (n.1). Meaning "semicircular bend in a river" is from 1797, American English (New England); meaning "curved lake left after an oxbow meander has been cut off by a change in the river course" is from 1898. The reference is to similarity of shape.
|oxbow lake |
A crescent-shaped lake formed when a river changes its course and cuts through the strip of land in the middle of an oxbow, abandoning its previous course and isolating the water in the oxbow.