extensor

 
Pronunciation: /ɪkˈstɛnsə, ɛk-/
(also extensor muscle)

noun

Anatomy
  • a muscle whose contraction extends or straightens a limb or other part of the body. Often contrasted with flexor.

Origin:

early 18th century: from late Latin, from extens- 'stretched out', from the verb extendere (see extend)