onwards vs ahead

onwards is not an adjective while ahead is an adjective.

Word	Noun	Adjective	Verb	Adverb
onwards	No	No	No	Yes
ahead	No	Yes	No	Yes

As adverbs, onwards and ahead are synonyms defined as:

Other synonyms of onwards include forrader, forward, forwards, onward.

onwards (adjective)	ahead (adjective)
	having the leading position or higher score in a contest

onwards (adverb)	ahead (adverb)
in a forward direction	at or in the front
	ahead of time; in anticipation
	in a forward direction
	leading or ahead in a competition
	to a different or a more advanced time (meaning advanced either toward the present or toward the future)
	to a more advanced or advantageous position
	toward the future; forward in time