downwind vs windward

downwind is not a noun while windward is a noun.

Word	Noun	Adjective	Verb	Adverb
downwind	No	Yes	No	Yes
windward	Yes	Yes	No	Yes

As adverbs, downwind and windward are synonyms defined as:

downwind (noun)	windward (noun)
	the side of something that is toward the wind
	the direction from which the wind is coming

downwind (adjective)	windward (adjective)
towards the side away from the wind	on the side exposed to the wind

downwind (adverb)	windward (adverb)
with the wind; in the direction the wind is blowing	toward the wind
toward the wind