assback means on the back of a donkey. Lexicurio rates it Rare gem — a strength score of 82 out of 100.
Etymology
From ass + back.
adv
- On the back of a donkey.“[…] I should have thought a great chief had something better to do than to play chess either horseback or assback.”
noun
- The back of a donkey.“1691, uncredited translators, Plutarch’s Morals, Part 2, London: T. Sawbridge et al., p. 224,
[…] they took her and set her on Ass-back, and led her round about the City,”