To make a voiced consonant sound voiceless (removing the vibration of vocal cords), such as changing a 'z' sound to an 's' sound.
From de- (remove) + voice, a phonetic term that emerged in early 20th-century linguistics to describe a specific speech transformation.
Languages like Russian actually devoice ALL their consonants at the end of words—so 'dog' and 'dock' sound identical in Russian, which trips up English speakers learning the language!
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