keep back vs immobilize

keep back and immobilize both are verbs.

Word	Noun	Adjective	Verb	Adverb
keep back	No	No	Yes	No
immobilize	No	No	Yes	No

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

Other hyponyms of keep back include block, freeze, immobilise, keep to oneself, deny, reserve, immobilise, deprive.

keep back (verb)	immobilize (verb)
prevent the action or expression of	cause to be unable to move
hold back; refuse to hand over or share	prohibit the conversion or use of (assets)
secure and keep for possible future use or application	convert (assets) into fixed capital
	make defenseless
	to hold fast or prevent from moving
	hold as reserve or withdraw from circulation; of capital