1817, first used by Arctic explorers, probably from Norwegian flo "layer, slab," from Old Norse flo, from PRoto-Germanic *floho-, from PIE *plak- (1) "to be flat," extended form of root *pele- (2) "flat, to spread" (see plane, n.1). Related to first element in flagstone. Earlier explorers used flake. Floe-rat was a seal-hunter's name for the ringed seal (1880).