drone vs drone on

drone is a noun but drone on is not a noun.

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

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

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