late 14c., noun of action from repress (v.), or else from Medieval Latin repressionem (nominative repressio), noun of action from past participle stem of Latin reprimere. Psychological sense is from 1908; biochemical sense is from 1957.
repression re·pres·sion (rĭ-prěsh'ən)
n.
The act of repressing or the state of being repressed.
The unconscious exclusion of painful impulses, desires, or fears from the conscious mind.