slip away vs lapse

slip away is not a noun while lapse is a noun.

Word	Noun	Adjective	Verb	Adverb
slip away	No	No	Yes	No
lapse	Yes	No	Yes	No

As verbs, slip away and lapse are synonyms defined as:

Other synonyms of slip away include elapse, glide by, go along, go by, pass, slide by, slip by.

slip away (noun)	lapse (noun)
	a mistake resulting from inattention
	a failure to maintain a higher state
	a break or intermission in the occurrence of something

slip away (verb)	lapse (verb)
for time to move forward	go back to bad behavior
leave furtively and stealthily	drop to a lower level, as in one's morals or standards
	end, at least for a long time
	for time to move forward
	pass into a specified state or condition; sink into
	let slip