O.E. -istre, from P.Gmc. *-istrijon, feminine agent suffix used as the equivalent of masculine -ere. Also used in M.E. to form nouns of action (meaning "a person who ...") without regard for gender. The genderless agent noun use apparently was a broader application of the original feminine suffix, beginning
in the north of England, but linguists disagree over whether this indicates female domination of weaving and baking trades, as represented in names like Webster, Baxter, Brewster, etc. (though spinster clearly represents a female ending). In Modern Eng., the suffix has been productive in forming derivative nouns (gamester, punster, etc.).