slip away vs vanish

slip away and vanish both are verbs.

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

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

Other hyponyms of slip away include fell, fly.

slip away (verb)	vanish (verb)
for time to move forward	get lost, as without warning or explanation
leave furtively and stealthily	decrease rapidly and disappear
	cease to exist
	pass away rapidly
	become invisible or unnoticeable