Radar

google

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1940s: from ra(dio) d(etection) a(nd) r(anging) .

wiktionary

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Originally spelled RADAR; an acronym of radio detection and ranging. Coined by the United States Navy in 1940.

etymonline

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radar (n.)

"electronic system for locating and tracking objects at a distance by means of radio waves," 1941, acronym (more or less) from radio detecting and ranging. The U.S. choice, it won out over British radiolocation. Figurative from 1950.