tertiary orifice
Basically, a woman’s asshole or anus may serve to be her third input, or tertiary orifice. A woman, being master of her own body, may deem whatever orifices she has to be primary, secondary or tertiary as she seems fit. For this definition, we have chosen the brown-eye.
“Annabel was both eager and anxious for me to ram my wad into her tertiary orifice. Sod.”