knock off is a verb meaning "get rid of (someone who may be a threat) by killing". It carries 5 recorded senses.
get rid of (someone who may be a threat) by killing
“The mafia liquidated the informer”
“the double agent was neutralized”
cut the price of
write quickly
“She dashed off a note to her husband saying she would not be home for supper”
“He scratched off a thank-you note to the hostess”
writing
stop pursuing or acting
“drop a lawsuit”
“knock it off!”
Definitions, synonyms and semantic relations for knock off come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.