slip away vs go away

slip away and go away both are verbs.

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

As verbs, go away is a hypernym of slip away; that is, go away is a word with a broader meaning than slip away:

Other hypernyms of slip away include go forth, leave.

slip away (verb)	go away (verb)
for time to move forward	get lost, as without warning or explanation
leave furtively and stealthily	go away from a place
	move away from a place into another direction
	become invisible or unnoticeable