at a loss

loss (lɒs)
—n
1.	the act or an instance of losing
2.	the disadvantage or deprivation resulting from losing: a loss of reputation
3.	the person, thing, or amount lost: a large loss
4.	(plural) military personnel lost by death or capture
5.	(sometimes plural) the amount by which the costs of a business transaction or operation exceed its revenue
6.	a measure of the power lost in an electrical system expressed as the ratio of or difference between the input power and the output power
7.	insurance
	a.  an occurrence of something that has been insured against, thus giving rise to a claim by a policyholder
	b.  the amount of the resulting claim
8.	at a loss
	a.  uncertain what to do; bewildered
	b.  rendered helpless (for lack of something): at a loss for words
	c.  at less than the cost of buying, producing, or maintaining (something): the business ran at a loss for several years
[C14: noun probably formed from lost, past participle of losen to perish, from Old English lōsian to be destroyed, from los destruction]

loss

loss

n. 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. Compare lossage.

at a loss

1. Below cost, as in The store was doing so badly that it was selling merchandise at a loss.

2. Puzzled, perplexed, in a state of uncertainty, as in When his letters were returned unopened, John was at a loss as to what to do next. This usage was originally applied to hounds who had lost the scent or track of their prey. [Mid-1600s]

3. at a loss for words. Unable or uncertain as to what to say. For example, Father's tirade left us all at a loss for words. [Late 1600s]