says E. Adams (English Language), properly means a bar—maid; “- ster” is the Anglo-Saxon feminine suffix —estre, which remains in spin-ster (a female spinner).
This is only a half-truth. After the thirteenth century, the suffix—ster was used for an agent of either sex. We have barrister, gamester, punster, etc., and Wickliffe uses songster for a male singer (See Dr. Morris Historic Outlines, p. 89.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894