Old English -istre, from Proto-Germanic *-istrijon, feminine agent suffix used as the equivalent of masculine -ere (see -er (1)). Also used in Middle English 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 surnames such as Webster, Baxter, Brewster, etc. (though spinster clearly represents a female ending). In Modern English, the suffix has been productive in forming derivative nouns (gamester, punster, etc.).
: That's stepping. Until recently, this dance form, which is said to have its roots in South African boot dances, has been performed only in African-American fraternities and sororities (1990s+)