c. 1600, "to be jovial and boisterous," also "to talk bombastically," from Dutch randten (earlier ranten) "talk foolishly, rave," of unknown origin (compare German rantzen "to frolic, spring about"). Related: Ranted; ranting. Ranters "antinomian sect which arose in England c. 1645" is attested from 1651; applied 1823 to early Methodists. A 1700 slang dictionary has rantipole "a rude wild Boy or Girl" (also as a verb and adjective); to ride rantipole meant "The woman uppermost in the amorous congress" [Grose].
Rant is extravagant or violent language, proceeding from or fanaticism, generally in support of extreme opinions against those holding opinions of a milder or different sort. [Century Dictionary, 1889]