move back vs retreat

move back is not a noun while retreat is a noun.

Word	Noun	Adjective	Verb	Adverb
move back	No	No	Yes	No
retreat	Yes	No	Yes	No

As verbs, move back and retreat are synonyms defined as:

Other synonyms of move back include draw back, pull away, pull back, recede, retire, withdraw.

As verbs, retreat is a hyponym of move back; that is, retreat is a word with a more specific, narrower meaning than move back:

Other hyponyms of move back include fall back, retrograde, back down, back off, back up.

move back (noun)	retreat (noun)
	(military) withdrawal of troops to a more favorable position to escape the enemy's superior forces or after a defeat
	withdrawal for prayer and study and meditation
	the act of withdrawing or going backward (especially to escape something hazardous or unpleasant)
	an area where you can be alone
	(military) a bugle call signaling the lowering of the flag at sunset
	(military) a signal to begin a withdrawal from a dangerous position
	a place of privacy; a place affording peace and quiet

move back (verb)	retreat (verb)
pull back or move away or backward	make a retreat from an earlier commitment or activity
	pull back or move away or backward
	move back
	move away, as for privacy