Is it ensure, insure, or assure?
c.1600, "to be jovial and boisterous," also "to talk bombastically," from Dutch randten (earlier ranten) "talk foolishly, rave," of unknown origin (cf. 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].
"boisterous, empty declamation; fierce or high-sounding language without much meaning or dignity of thought; bombast; a ranting speech," 1640s, from rant (v.).