left, adj. /lɛft/
From the simple past tense form of “to leave.” In the early days of English theatre, all actors would enter from one side of a proscenium stage and exit on the other. When an actor had left the stage, they were said to be “stage left,” regardless of which particular side it was for that particular stage. The side designations were standardized just in time for the popularity of the Lord Chamberlain’s Men at the Globe Theatre (a theatre in the round) to render them unfashionable.