"place or opening by which anything is let out or escapes," mid-13c., "a river mouth," from out- + let (v.). Electrical wiring sense, "socket that connects a device to an electricity supply," is attested from 1892. The commercial sense of "a market for the sale of any product" is by 1889; that of "a retail store disposing of a manufacturer's products" is attested by 1933. Figurative sense "means of relief or discharge" is from 1620s.
"of or pertaining to sale, sales, or the business of selling," word-forming element from genitive of sale (n.), by 1520s, in salesman. Cf. saleswork "work done for sale" (1775). For earlier use of similar formations, compare craftsman, oarsman, both Middle English. Sales tax is attested by 1886; sales clerk by 1863; sales associate by 1946. Sales representative is from 1910.
"action of selling," early 14c., verbal noun from sell (v.). Selling-point is attested from 1953 as "retail outlet;" by 1959 as "persuasive fact in a sales pitch."
"sluggish watercourse, outlet of a lake or river," 1766, American English, via Louisiana French, from Choctaw (Muskogean) bayuk "small stream."
1949, perhaps from Creole French pronunciation of French les haricots "the beans," part of the title of a popular dance tune ("les haricots sont pas salés").