flycatcher vs thickhead

flycatcher and thickhead both are nouns.

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

As nouns, thickhead is a hyponym of flycatcher; that is, thickhead is a word with a more specific, narrower meaning than flycatcher:

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

Other hyponyms of flycatcher include Muscicapa grisola, Muscicapa striata, spotted flycatcher, whistler.

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