"Tòn agus druim."

Translation: Buttocks and back.

[OmBacon]

Surely this a buttock and tòin would be buttocks?

[silmeth]

tòn is bottom, backside, bum, arse, buttock(s); translating it as buttocks, I guess, is just an euphemism to not write too impolite English.

And plural of that is tònan.

See entries for the word in AFB, Dwelly, and Wiktionary.