slip by vs fell

slip by is not a noun while fell is a noun.

Word	Noun	Adjective	Verb	Adverb
slip by	No	No	Yes	No
fell	Yes	Yes	Yes	No

As verbs, fell is a hyponym of slip by; that is, fell is a word with a more specific, narrower meaning than slip by:

Other hyponyms of slip by include fly, vanish.

slip by (noun)	fell (noun)
	the act of felling something (as a tree)
	seam made by turning under or folding together and stitching the seamed materials to avoid rough edges
	the dressed skin of an animal (especially a large animal)

slip by (adjective)	fell (adjective)
	(of persons or their actions) able or disposed to inflict pain or suffering

slip by (verb)	fell (verb)
for time to move forward	cause to fall by or as if by delivering a blow
	sew a seam by folding the edges
	pass away rapidly