tremble vs reflex action

tremble and reflex action both are nouns.

Word	Noun	Adjective	Verb	Adverb
tremble	Yes	No	Yes	No
reflex action	Yes	No	No	No

As nouns, reflex action is a hypernym of tremble; that is, reflex action is a word with a broader meaning than tremble:

tremble (noun)	reflex action (noun)
a reflex motion caused by cold or fear or excitement	an automatic instinctive unlearned reaction to a stimulus

tremble (verb)	reflex action (verb)
move or jerk quickly and involuntarily up and down or sideways