cost vs knock back

cost is a noun but knock back is not a noun.

Word	Noun	Adjective	Verb	Adverb
cost	Yes	No	Yes	No
knock back	No	No	Yes	No

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

Other hyponyms of cost include put back, set back.

cost (noun)	knock back (noun)
the property of having material worth (often indicated by the amount of money something would bring if sold)
value measured by what must be given or done or undergone to obtain something
the total spent for goods or services including money and time and labor

cost (verb)	knock back (verb)
be priced at	cost a certain amount
require to lose, suffer, or sacrifice