Green’s Dictionary of Slang

arse-end n.

also ass-end
[arse n. (1) + SE end]

1. [1930s+] the end, the rear end, the buttocks.

2. [1940s+] a very unappealing place, particularly one far away from ‘civilization’; esp. in phr. arse-end of the universe, arse-end of nowhere.