they took turns stopping at frequent intervals to relieve themselves, allowing me to dismount for a few minutes and surreptitiously rub my aching fundament.
Diana Gabaldon. Outlander (1991)
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Rachel stood outside the lav door and smiled. I came from the buffet to join her.
"What's wrong in there?" I asked my flying partner.
"It's a woman. She says she's stuck."
"Stuck?" "What's stuck?"
Rachel started to giggle.
"You mean her fundament?"
Trudy Baker and Rachel Jones. Coffee Tea or Me (1967)
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But when the disease was more stubborn and violent, he let in the muzzle while the bellows were full of wind, which he discharged into the body of the patient; then withdrew the instrument to replenish it, clapping his thumb strongly against the orifice of then fundament; and this being repeated three or four times, the adventitious wind would rush out, bringing the noxious along with it, (like water put into a pump),
Jonathan Swift. Gulliver's Travels Into Several Remote Regions of the World (1726)