flatfoot vs human foot

flatfoot and human foot both are nouns.

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

As nouns, human foot is a hypernym of flatfoot; that is, human foot is a word with a broader meaning than flatfoot:

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

Other hypernyms of flatfoot include foot, pes.

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