chestnut oak vs oak

chestnut oak and oak both are nouns.

Word	Noun	Adjective	Verb	Adverb
chestnut oak	Yes	No	No	No
oak	Yes	No	No	No

As nouns, oak is a hypernym of chestnut oak; that is, oak is a word with a broader meaning than chestnut oak:

Other hypernyms of chestnut oak include oak tree.

chestnut oak (noun)	oak (noun)
an oak having leaves resembling those of chestnut trees	a deciduous tree of the genus Quercus; has acorns and lobed leaves
	the hard durable wood of any oak; used especially for furniture and flooring