tokonoma baseboard; alcove slab
Specifically the wooden board placed at the bottom of a tokonoma (alcove). Not a general floorboard.
See also: 床の間
We replaced the baseboard of the tokonoma.
Compound of 床 (とこ, 'alcove') + 板 (いた, 'board'). The reading とこ is specific to the tokonoma context.