single out vs separate

single out is not a noun while separate is a noun.

Word	Noun	Adjective	Verb	Adverb
single out	No	No	Yes	No
separate	Yes	Yes	Yes	No

As verbs, single out and separate are synonyms defined as:

Other synonyms of single out include discriminate.

As verbs, separate is a hypernym of single out; that is, separate is a word with a broader meaning than single out:

Other hypernyms of single out include differentiate, distinguish, secern, secernate, severalise, severalize, tell, tell apart.

single out (noun)	separate (noun)
	a garment that can be purchased separately and worn in combinations with other garments
	a separately printed article that originally appeared in a larger publication

single out (adjective)	separate (adjective)
	independent; not united or joint
	standing apart; not attached to or supported by anything
	separated according to race, sex, class, or religion
	have the connection undone; having become separate

single out (verb)	separate (verb)
select from a group	become separated into pieces or fragments
treat differently on the basis of sex or race	divide into two or more branches so as to form a fork
	arrange or order by classes or categories
	mark as different
	move or break apart
	force, take, or pull apart
	divide into components or constituents
	go one's own way; move apart
	make a division or separation
	treat differently on the basis of sex or race
	separate into parts or portions
	discontinue an association or relation; go different ways
	act as a barrier between; stand between