Definition of: turnstile

(tûrn′stīl′) noun
1. A kind of gate or closure consisting of a vertical post and horizontal arms which by revolving permit persons, but not cattle, to pass; also, one that permits persons to pass in one direction only.
2. A similar device for registering the number of persons entering a building or for automatically admitting passengers to subways, buses, etc., on the deposit of fares.