knee-jerk reflex vs reflex

knee-jerk reflex and reflex both are nouns.

Word	Noun	Adjective	Verb	Adverb
knee-jerk reflex	Yes	No	No	No
reflex	Yes	Yes	No	No

As nouns, reflex is a hypernym of knee-jerk reflex; that is, reflex is a word with a broader meaning than knee-jerk reflex:

knee-jerk reflex: a reflex extension of the leg resulting from a sharp tap on the patellar tendon
reflex: an automatic instinctive unlearned reaction to a stimulus

knee-jerk reflex (noun)	reflex (noun)
a reflex extension of the leg resulting from a sharp tap on the patellar tendon	an automatic instinctive unlearned reaction to a stimulus

knee-jerk reflex (adjective)	reflex (adjective)
	without volition or conscious control