army unit vs foot

army unit and foot both are nouns.

Word	Noun	Adjective	Verb	Adverb
army unit	Yes	No	No	No
foot	Yes	No	Yes	No

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

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