The Collaborative International Dictionary of English v.0.48:

Baseboard \Base"board\, n. (Arch.)
   A board, or other woodwork, carried round the walls of a room
   and touching the floor, to form a base and protect the
   plastering; -- also called washboard (in England), mopboard,
   and scrubboard.
   [1913 Webster]

WordNet (r) 3.0 (2006):

baseboard
    n 1: a molding covering the joint formed by a wall and the floor
         [syn: baseboard, mopboard, skirting board]