tell apart vs separate

tell apart is not a noun while separate is a noun.

Word	Noun	Adjective	Verb	Adverb
tell apart	No	No	Yes	No
separate	Yes	Yes	Yes	No

As verbs, tell apart and separate are synonyms defined as:

Other synonyms of tell apart include differentiate, distinguish, secern, secernate, severalise, severalize, tell.

As verbs, separate is a hyponym of tell apart; that is, separate is a word with a more specific, narrower meaning than tell apart:

tell apart (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

tell apart (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

tell apart (verb)	separate (verb)
mark as different	become separated into pieces or fragments
detect with the senses	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