rearward vs backward

rearward is a noun but backward is not a noun.

Word	Noun	Adjective	Verb	Adverb
rearward	Yes	Yes	No	Yes
backward	No	Yes	No	Yes

As adverbs, rearward and backward are synonyms defined as:

Other synonyms of rearward include back, backwards, rearwards.

rearward (noun)	backward (noun)
direction toward the rear

rearward (adjective)	backward (adjective)
located in or toward the back or rear	directed or facing toward the back or rear
directed or moving toward the rear	(used of temperament or behavior) marked by a retiring nature
	retarded in intellectual development
	having made less than normal progress

rearward (adverb)	backward (adverb)
at or to or toward the back or rear	in a manner or order or direction the reverse of normal
	in or to or toward a past time
	at or to or toward the back or rear