drone on vs drone

drone on is not a noun while drone is a noun.

Word	Noun	Adjective	Verb	Adverb
drone on	No	No	Yes	No
drone	Yes	No	Yes	No

As verbs, drone on and drone are synonyms defined as:

drone on (noun)	drone (noun)
	stingless male bee in a colony of social bees (especially honeybees) whose sole function is to mate with the queen
	a pipe of the bagpipe that is tuned to produce a single continuous tone
	an aircraft without a pilot that is operated by remote control
	an unchanging intonation
	someone who takes more time than necessary; someone who lags behind

drone on (verb)	drone (verb)
talk in a monotonous voice	talk in a monotonous voice
	make a monotonous low dull sound