also lock-out, "act of excluding from a place by locking it up," especially of management locking out workers in labor disputes (1854) but also in 19c. the exclusion of a teacher from the schoolhouse by his pupils as an act of protest. From the verbal phrase lock (someone) out, which is attested from mid-14c. in the sense "turn or keep out (of a place), bar the doors against" (see lock (v.) + out (adv.)).