yawn vs physiological reaction

yawn and physiological reaction both are nouns.

Word	Noun	Adjective	Verb	Adverb
yawn	Yes	No	Yes	No
physiological reaction	Yes	No	No	No

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

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