foot up vs foot

foot up is not a noun while foot is a noun.

Word	Noun	Adjective	Verb	Adverb
foot up	No	No	Yes	No
foot	Yes	No	Yes	No

As verbs, foot up and foot are synonyms defined as:

foot up (noun)	foot (noun)
	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