oak tree vs oak

oak tree and oak both are nouns.

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

As nouns, oak tree and oak are synonyms defined as:

oak tree and oak: a deciduous tree of the genus Quercus; has acorns and lobed leaves

oak tree (noun)	oak (noun)
a deciduous tree of the genus Quercus; has acorns and lobed leaves	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