human foot vs flatfoot

human foot and flatfoot both are nouns.

Word	Noun	Adjective	Verb	Adverb
human foot	Yes	No	No	No
flatfoot	Yes	No	No	No

As nouns, flatfoot is a hyponym of human foot; that is, flatfoot is a word with a more specific, narrower meaning than human foot:

human foot: the part of the leg of a human being below the ankle joint
flatfoot: a foot afflicted with a fallen arch; abnormally flattened and spread out

Other hyponyms of human foot include pes planus, splayfoot.

human foot (noun)	flatfoot (noun)
the part of the leg of a human being below the ankle joint	a foot afflicted with a fallen arch; abnormally flattened and spread out
	a policeman who patrols a given region