Past tense of radio: to send a message using radio waves or to communicate by radio.
From 'radio' (from Latin 'radius', ray or spoke), which was invented in the 1800s. The verb form '-ed' makes it past tense, becoming common once radio communication became widespread.
Radio as a verb is relatively new—it only makes sense after radios became common devices, showing how technologies literally create new verbs (we didn't 'radio' anyone before the 1920s, just like we didn't 'email' anyone before 1990).
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