call back vs call-back

call back is not a noun while call-back is a noun.

Word	Noun	Adjective	Verb	Adverb
call back	No	No	Yes	No
call-back	Yes	No	No	No

call back (noun)	call-back (noun)
	the recall of an employee after a layoff
	a return call

call back (verb)	call-back (verb)
recall knowledge from memory; have a recollection
summon to return
return or repeat a telephone call
cause to be returned