'blackout' originates from English, specifically a compound of the words 'black' and 'out', where 'black' comes from Old English 'blæc' meaning 'black/dark' and 'out' comes from Old English 'ūt' meaning 'out'.

'blackout' developed from the phrasal verb 'black out' (formed from 'black' + 'out') and came into use as a noun and verb in modern English; the noun sense 'a period of darkness or power loss' became especially common in the early 20th century (notably in wartime blackout regulations) and the medical sense 'loss of consciousness or memory' attested around the late 19th to early 20th century.

Initially it meant 'to make dark' or 'put out light'; over time it broadened to mean 'a temporary loss of electrical power', 'a loss of consciousness or memory', and also 'a broadcast restriction or censorship'.