mark up vs markup

mark up is not a noun while markup is a noun.

Word	Noun	Adjective	Verb	Adverb
mark up	No	No	Yes	No
markup	Yes	No	No	No

mark up (noun)	markup (noun)
	detailed stylistic instructions for typesetting something that is to be printed; manual markup is usually written on the copy (e.g. underlining words that are to be set in italics)
	the amount added to the cost to determine the asking price

mark up (verb)	markup (verb)
increase the price of