shiver vs reflex response

shiver and reflex response both are nouns.

Word	Noun	Adjective	Verb	Adverb
shiver	Yes	No	Yes	No
reflex response	Yes	No	No	No

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

shiver (noun)	reflex response (noun)
a reflex motion caused by cold or fear or excitement	an automatic instinctive unlearned reaction to a stimulus
an almost pleasurable sensation of fright

shiver (verb)	reflex response (verb)
shake, as from cold
tremble convulsively, as from fear or excitement