overcup oak vs oak tree

overcup oak and oak tree both are nouns.

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

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

overcup oak: medium-large deciduous timber tree of central and southern United States; acorns deeply immersed in the cup and mature in first year
oak tree: a deciduous tree of the genus Quercus; has acorns and lobed leaves

Other hypernyms of overcup oak include oak.

overcup oak (noun)	oak tree (noun)
medium-large deciduous timber tree of central and southern United States; acorns deeply immersed in the cup and mature in first year	a deciduous tree of the genus Quercus; has acorns and lobed leaves