Green’s Dictionary of Slang

(orig. US) anilingus.

1979		Maledicta III:2 218: Australian = anilinctus practitioner (rimming from Down Under).
1985		K. Vacha Quiet Fire 45: Rimming wasn’t a big thing in the United States after the war.
1985		‘Thommo’ Dict. Aus. Swearing & Sex Sayings 110: RIMMING — Analingus, oral anal stimulation.
2003		Backlash29 ‘swimslut’ on Nifty Erotic Stories Archive 🌐 Chris was a serious rimmer, and within seconds he had squished his entire tongue into Ben’s clean, tasty hole and was swabbing it around. Savoring the heavenly rimming, Ben relaxed.