hereinafter vs hereafter

hereinafter is not a noun while hereafter is a noun.

Word	Noun	Adjective	Verb	Adverb
hereinafter	No	No	No	Yes
hereafter	Yes	No	No	Yes

As adverbs, hereinafter and hereafter are synonyms defined as:

hereinafter and hereafter: in a subsequent part of this document or statement or matter etc.

Other synonyms of hereinafter include hereunder.

hereinafter (noun)	hereafter (noun)
	the time yet to come
	life after death

hereinafter (adverb)	hereafter (adverb)
in a subsequent part of this document or statement or matter etc.	in a subsequent part of this document or statement or matter etc.
	following this in time or order or place; after this
	in a future life or state