rant vs rabbit on

rant is a noun but rabbit on is not a noun.

Word	Noun	Adjective	Verb	Adverb
rant	Yes	No	Yes	No
rabbit on	No	No	Yes	No

As verbs, rant and rabbit on are synonyms defined as:

Other synonyms of rant include jabber, mouth off, rave, spout.

rant (noun)	rabbit on (noun)
pompous or pretentious talk or writing
a loud bombastic declamation expressed with strong emotion

rant (verb)	rabbit on (verb)
talk in a noisy, excited, or declamatory manner	talk in a noisy, excited, or declamatory manner