shiver vs reflex

shiver and reflex both are nouns.

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

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

shiver (noun)	reflex (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 (adjective)	reflex (adjective)
	without volition or conscious control

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