exterminate vs kill off

exterminate and kill off both are verbs.

Word	Noun	Adjective	Verb	Adverb
exterminate	No	No	Yes	No
kill off	No	No	Yes	No

As verbs, exterminate and kill off are synonyms defined as:

exterminate and kill off: kill en masse; kill on a large scale; kill many

exterminate (verb)	kill off (verb)
kill en masse; kill on a large scale; kill many	kill en masse; kill on a large scale; kill many
destroy completely, as if down to the roots