in all likelihood vs likely

in all likelihood is not an adjective while likely is an adjective.

Word	Noun	Adjective	Verb	Adverb
in all likelihood	No	No	No	Yes
likely	No	Yes	No	Yes

As adverbs, in all likelihood and likely are synonyms defined as:

in all likelihood and likely: with considerable certainty; without much doubt

Other synonyms of in all likelihood include belike, in all probability, probably.

in all likelihood (adjective)	likely (adjective)
	has a good chance of being the case or of coming about
	within the realm of credibility
	expected to become or be; in prospect

in all likelihood (adverb)	likely (adverb)
with considerable certainty; without much doubt	with considerable certainty; without much doubt