Why is a restaurant bill called a "check"?
Why is a restaurant bill called a "check" (as in "Check, please!")?
This is a good question, and the general references (Online Etymology Dictionary, etc.) are not helpful in getting a definite answer. That is, they give the general etymology of check (it arose from chess, and "All the other senses seem to have developed from this one"), but not of this particular "restaurant bill" sense. Even the Oxford English Dictionary does not explain it; however its classification is suggestive. It says:
14. A means to ensure accuracy, correctness, security from fraud, etc.: as
†a. The counterfoil of a bank bill, draft, etc.
.
b. A token, usually a memorandum of receipt, a ticket, or piece of metal […] used for the purpose of identification, or as evidence of ownership or title: given, e.g. to the owner of luggage on a railway (as in U.S.), or to one who temporarily leaves luggage, cloaks, […] etc., etc.
.
c. A restaurant bill. Chiefly U.S.
1869 A. D. Whitney … I let her settle for the dinner checks.
1910 ‘O. Henry’ … Through an arched opening‥you thrust your waiter's check and the money.
1916 Variety … Inspectors‥ordered drinks and paid their check just before one.
1937 R. Stout … I‥found the waitress and got my check from her.
(Looking under cheque, it seems to have arisen as "a differentiated spelling" of check in sense 14a, so the modern meaning of cheque (or American [bank] check) is different from 14c.)
So to answer your question, we don't know exactly, but the heading under which the OED has put the word suggests that they think it came from "a means to ensure (check) correctness". It's not entirely clear what the restaurant bill is meant to check (perhaps the diner checks that he/she is being asked for the correct amount). This listing is still not as definite as an explicit pronouncement on the origin of this sense, so something concrete from a real expert would be useful.
In the etymonline entry for check you can find:
c.1700 "a token used to check against loss or theft" (surviving in hat check)
Maybe it was first used to call the waiter to bring you your hat (coat, cane, etc.) and the bill; in the "olden" days, when it was customary to wear hats, it was not unusual for restaurants to have hat racks at which people would leave their hats.
Another possibility is that the guest wanted to check the bill, before paying for it.
No references to support either theory.