"a public address; a formal, vehement, or passionate address;" also "any formal or pompous speech; a declamation; a tirade," mid-15c., arang, Scottish (in English from c. 1600), from French harangue "a public address" (14c.), from Old Italian aringo "public square, platform; pulpit; arena," from a Germanic source such as Old High German hring "circle" (see ring (n.1)) on the notion of "circular gathering," with an -a- inserted to ease Romanic pronunciation of Germanic hr- (compare hamper (n.1)).
But Watkins and Barnhart suggest a Germanic compound, *harihring "circular gathering, assembly," literally "host-ring, army-ring," with first element *hari- "war-band, host" (see harry (v.)). From the same Germanic "ring" root via Romanic come rank (n.), range (v.), arrange.
"to address in a harangue; to deliver a harangue," 1650s, from French haranguer (15c.), from harangue (see harangue (n.)). Related: Harangued; haranguing.