oscitance vs drowsiness

oscitance and drowsiness both are nouns.

Word	Noun	Adjective	Verb	Adverb
oscitance	Yes	No	No	No
drowsiness	Yes	No	No	No

As nouns, drowsiness is a hypernym of oscitance; that is, drowsiness is a word with a broader meaning than oscitance:

Other hypernyms of oscitance include dullness, obtuseness, sleepiness, somnolence.

oscitance (noun)	drowsiness (noun)
an involuntary intake of breath through a wide open mouth; usually triggered by fatigue or boredom	a very sleepy state
drowsiness and dullness manifested by yawning