bird's foot vs foot

bird's foot and foot both are nouns.

As nouns, foot is a hypernym of bird's foot; that is, foot is a word with a broader meaning than bird's foot:

Other hypernyms of bird's foot include animal foot.

bird's foot (noun)	foot (noun)
the foot of a bird	the part of the leg of a human being below the ankle joint
	a linear unit of length equal to 12 inches or a third of a yard
	the lower part of anything
	the pedal extremity of vertebrates other than human beings
	lowest support of a structure
	any of various organs of locomotion or attachment in invertebrates
	travel by walking
	a member of a surveillance team who works on foot or rides as a passenger
	an army unit consisting of soldiers who fight on foot
	(prosody) a group of 2 or 3 syllables forming the basic unit of poetic rhythm
	a support resembling a pedal extremity