white out vs whiteout

white out is not a noun while whiteout is a noun.

Word	Noun	Adjective	Verb	Adverb
white out	No	No	Yes	No
whiteout	Yes	No	Yes	No

As verbs, white out and whiteout are synonyms defined as:

white out (noun)	whiteout (noun)
	an arctic atmospheric condition with clouds over snow produce a uniform whiteness and objects are difficult to see; occurs when the light reflected off the snow equals the light coming through the clouds

white out (verb)	whiteout (verb)
widen the interlinear spacing by inserting leads	lose daylight visibility in heavy fog, snow, or rain
cover up with a liquid correction fluid	cover up with a liquid correction fluid