slip away vs pass

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

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

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

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

slip away (noun)	pass (noun)
	(sports) the act of throwing the ball to another member of your team
	a usually brief attempt
	(American football) a play that involves one player throwing the ball to a teammate
	(baseball) an advance to first base by a batter who receives four balls
	success in satisfying a test or requirement
	a flight or run by an aircraft over a target
	a permit to enter or leave a military installation
	any authorization to pass or go somewhere
	an automatic advance to the next round in a tournament without playing an opponent
	a document indicating permission to do something without restrictions
	a complimentary ticket
	a difficult juncture
	one complete cycle of operations (as by a computer)
	the location in a range of mountains of a geological formation that is lower than the surrounding peaks
	a bad or difficult situation or state of affairs
	(military) a written leave of absence

slip away (adjective)	pass (adjective)
	of advancing the ball by throwing it

slip away (verb)	pass (verb)
for time to move forward	eliminate from the body
leave furtively and stealthily	come to pass
	disappear gradually
	pass from physical life and lose all bodily attributes and functions necessary to sustain life
	grant authorization or clearance for
	transmit information
	pass over, across, or through
	go across or through
	travel past
	pass into a specified state or condition; sink into
	for time to move forward
	cause to pass
	move past
	place into the hands or custody of
	throw (a ball) to another player
	transfer to another; of rights or property
	be inherited by
	make laws, bills, etc. or bring into effect by legislation
	go unchallenged; be approved
	accept or judge as acceptable
	go successfully through a test or a selection process
	allow to go without comment or censure
	use up a period of time in a specific way
	be superior or better than some standard
	stretch out over a distance, space, time, or scope; run or extend between two points or beyond a certain point