cop vs knock off

cop is a noun but knock off is not a noun.

Word	Noun	Adjective	Verb	Adverb
cop	Yes	No	Yes	No
knock off	No	No	Yes	No

As verbs, cop and knock off are synonyms defined as:

Other synonyms of cop include glom, hook, snitch, thieve.

cop (noun)	knock off (noun)
uncomplimentary terms for a policeman

cop (verb)	knock off (verb)
take into custody	stop pursuing or acting
take by theft	get rid of (someone who may be a threat) by killing
	write quickly
	take by theft
	cut the price of