prop vs prop up

prop is a noun but prop up is not a noun.

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

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

Other synonyms of prop include shore, shore up.

prop (noun)	prop up (noun)
a support placed beneath or against something to keep it from shaking or falling
a propeller that rotates to push against air
any movable articles or objects used on the set of a play or movie

prop (verb)	prop up (verb)
support by placing against something solid or rigid	support by placing against something solid or rigid