Old English hyrnet, hurnitu "large wasp, beetle, gadfly," probably from Proto-Germanic *hurz-nut- (source also of Old Saxon hornut; Middle Dutch huersel, Dutch horzel (with diminutive suffix); Old High German hornaz, German Hornisse "hornet"), from a PIE imitative (buzzing) root; compare Old Church Slavonic srusa, Lithuanian širšu "wasp." On this theory, the English word (as well as German Hornisse) was altered by influence of horn, to suggest either "horner" (from the sting) or "horn-blower" (from the buzz). Compare also Old Saxon hornobero "hornet," literally "trumpeter." Figurative of troublesome and persistent attacks.
c. 1300, from Old French ire "anger, wrath, violence" (11c.), from Latin ira "anger, wrath, rage, passion," from PIE root *eis- (1), forming various words denoting passion (source also of Greek hieros "filled with the divine, holy," oistros "gadfly," originally "thing causing madness;" Sanskrit esati "drives on," yasati "boils;" Avestan aesma "anger;" Lithuanian aistra "violent passion").
Old English irre in a similar sense is unrelated; it is from an adjective irre "wandering, straying, angry," which is cognate with Old Saxon irri "angry," Old High German irri "wandering, deranged," also "angry;" Gothic airzeis "astray," and Latin errare "wander, go astray, angry" (see err (v.)).