General English


  • noun (a person) displaying a reflex action, an unthinking, automatic reaction. This piece of American slang of the early 1970s has passed into general colloquial use since its adoption as part of disparaging descriptions such as ‘knee-jerk liberal’ or ‘knee-jerk reactionary’. The expression of course derives from the doctors’ testing of the patellar reflex, featured in cartoons and situation comedies since the mid-1950s.