screw up vs muff

screw up is not a noun while muff is a noun.

Word	Noun	Adjective	Verb	Adverb
screw up	No	No	Yes	No
muff	Yes	No	Yes	No

As verbs, screw up and muff are synonyms defined as:

screw up (noun)	muff (noun)
	(sports) dropping the ball
	a warm tubular covering for the hands

screw up (verb)	muff (verb)
twist into a strained configuration	make a mess of, destroy or ruin
make more intense	fail to catch, as of a ball
screw or turn higher
make a mess of, destroy or ruin