/ ɪkˈstensə(r); BrE also ekˈs-; NAmE -sɔːr/ (also exˈtensor muscle ) noun
( anatomy ) a muscle that allows you to make part of your body straight or stretched out
—compare flexor
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WORD ORIGIN
early 18th cent.: from late Latin , from extens- stretched out, from the verb extendere stretch out, from ex- out + tendere stretch.