Borrowed from Old Norse Sleipnir (“the slipper, the slippy one”).
IPA(key): /ˈsleipnɪr/
Sleipnir
- (Norse mythology) The eight-legged horse of Odin.
1866, Charles Kingsley, chapter 33, in Hereward the Wake, London: Nelson, page 443:And Ranald swore first by the white Christ, and then by the head of Sleipnir, Odin’s horse[.]