onward vs ahead

onward is not an adjective while ahead is an adjective.

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

As adverbs, onward and ahead are synonyms defined as:

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

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

onward (adverb)	ahead (adverb)
forward in time or order or degree	at or in the front
in a forward direction	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