hamstring
noun /ˈhæmstrɪŋ/
  /ˈhæmstrɪŋ/
 - one of the five tendons behind the knee that connect the muscles of the upper leg to the bones of the lower leg- a hamstring injury
- She's pulled a hamstring.
 
- a tendon behind the hock (= middle joint) of the back leg of a horse and some other animals
Word Origin16th cent.: from ham ‘back of the thigh’ + string.