scrub oak vs oak

scrub oak and oak both are nouns.

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

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

scrub oak: any of various chiefly American small shrubby oaks often a dominant form on thin dry soils sometimes forming dense thickets
oak: a deciduous tree of the genus Quercus; has acorns and lobed leaves

Other hypernyms of scrub oak include oak tree.

scrub oak (noun)	oak (noun)
any of various chiefly American small shrubby oaks often a dominant form on thin dry soils sometimes forming dense thickets	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