Is it ensure, insure, or assure?
Old English los "loss, destruction," from Proto-Germanic *lausa- (see lose). The modern word, however, probably evolved 14c. with a weaker sense, from lost, the original past participle of lose. Phrase at a loss (1590s) originally refers to hounds losing the scent. To cut (one's) losses is from 1885, originally in finance.
Something (not a person) that loses; a situation in which something is losing. Emphatic forms include "moby loss", and "total loss", "complete loss". Common interjections are "What a loss!" and "What a moby loss!" Note that "moby loss" is OK even though **"moby loser" is not used; applied to an abstract noun, moby is simply a magnifier, whereas when applied to a person it implies substance and has positive connotations.