Definition from Wiktionary, the free dictionary
See also: turn-stile
turnstile (plural turnstiles)
- A rotating mechanical device that controls and counts passage between public areas, especially one that only allows passage after a charge has been made.
- (mathematics, logic) The symbol used to represent logical entailment (deducibility relation), especially of the syntactic type, i.e., syntactic consequence. (Such symbol can be read as "prove(s)"  or "give(s)." )
- (mathematics, logic): double turnstile
rotating mechanical device