lights-out
UK[ˌlaɪts ˈaʊt]US[ˌlaɪts ˈaʊt]
n
a signal (such as a bell or bugle call) given at night in a barracks or dormitory to indicate that lights are to be put out and silence is to be observed.
n
a time when this signal is given.
n
the end of activity or operation for the day; a stopping point.
n
(sports, informal) a knockout in boxing.
Etymology
the term "lights-out" is a modern english compound formed from two native germanic elements. the first part, "light," traces back to proto-germanic leuhtą and ultimately to the pie root leuk-, meaning "light, brightness." the second part, "out," originates from proto-germanic ūt and pie úd, meaning "upwards, away." the compound's literal sense, "lights extinguished," emerged from military and institutional routines where a signal mandated the extinguishing of lamps for sleep. this concrete meaning evolved metaphorically to signify the end of any activity or operation, and in boxing slang, it vividly denotes rendering an opponent unconscious, as if turning off their lights.
Analysis
the compound is formed from two english words: "lights" (plural of 'light', from old english 'lēoht', meaning illumination) and "out" (from old english 'ūt', meaning external, away, or extinguished). it functions as a fixed lexical unit, typically a noun.
Examples
the soldier hurried back to his bunk at the sound of lights-out.
lights-out for the factory is at midnight.
the champion delivered a punch that resulted in a dramatic lights-out in the first round.