true flycatcher vs oscine bird

true flycatcher and oscine bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
true flycatcher	Yes	No	No	No
oscine bird	Yes	No	No	No

As nouns, oscine bird is a hypernym of true flycatcher; that is, oscine bird is a word with a broader meaning than true flycatcher:

true flycatcher: any of a large group of small songbirds that feed on insects taken on the wing
oscine bird: passerine bird having specialized vocal apparatus

Other hypernyms of true flycatcher include oscine.

true flycatcher (noun)	oscine bird (noun)
any of a large group of small songbirds that feed on insects taken on the wing	passerine bird having specialized vocal apparatus