on an individual basis vs severally

on an individual basis and severally both are adverbs.

Word	Noun	Adjective	Verb	Adverb
on an individual basis	No	No	No	Yes
severally	No	No	No	Yes

As adverbs, on an individual basis and severally are synonyms defined as:

Other synonyms of on an individual basis include individually, one by one, separately, singly.

on an individual basis (adverb)	severally (adverb)
apart from others	apart from others
	individually or separately
	in the order given