crosswise vs across

crosswise is an adjective but across is not an adjective.

Word	Noun	Adjective	Verb	Adverb
crosswise	No	Yes	No	Yes
across	No	No	No	Yes

As adverbs, crosswise and across are synonyms defined as:

Other synonyms of crosswise include crossways.

crosswise (adjective)	across (adjective)
lying or extending across the length of a thing or in a cross direction
in the shape of (a horizontal piece on) a cross

crosswise (adverb)	across (adverb)
transversely	transversely
not in the intended manner	to the opposite side