slip away vs march on

slip away and march on both are verbs.

Word	Noun	Adjective	Verb	Adverb
slip away	No	No	Yes	No
march on	No	No	Yes	No

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

Other hypernyms of slip away include advance, go on, move on, pass on, progress.

slip away (verb)	march on (verb)
for time to move forward	move forward, also in the metaphorical sense
leave furtively and stealthily