yawn vs reflex

yawn and reflex both are nouns.

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

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

yawn: an involuntary intake of breath through a wide open mouth; usually triggered by fatigue or boredom
reflex: an automatic instinctive unlearned reaction to a stimulus

yawn (noun)	reflex (noun)
an involuntary intake of breath through a wide open mouth; usually triggered by fatigue or boredom	an automatic instinctive unlearned reaction to a stimulus

yawn (adjective)	reflex (adjective)
	without volition or conscious control

yawn (verb)	reflex (verb)
utter a yawn, as from lack of oxygen or when one is tired
be wide open