yawn vs reflex action

yawn and reflex action both are nouns.

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

As nouns, reflex action is a hypernym of yawn; that is, reflex action 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 action: an automatic instinctive unlearned reaction to a stimulus

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