thickhead vs flycatcher

thickhead and flycatcher both are nouns.

Word	Noun	Adjective	Verb	Adverb
thickhead	Yes	No	No	No
flycatcher	Yes	No	No	No

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

thickhead: Australian and southeastern Asian birds with a melodious whistling call
flycatcher: any of a large group of small songbirds that feed on insects taken on the wing

Other hypernyms of thickhead include Old World flycatcher, true flycatcher.

thickhead (noun)	flycatcher (noun)
Australian and southeastern Asian birds with a melodious whistling call	any of a large group of small songbirds that feed on insects taken on the wing
	large American birds that characteristically catch insects on the wing