• (n.) A bedplate; as, the soleplate of a steam engine. • (n.) The plate forming the back of a waterwheel bucket.
Sole'plate` noun (Machinery) (a) A bedplate; as, the soleplate of a steam engine. (b) The plate forming the back of a waterwheel bucket. 
A horizontal timber member fixed to the ground floor slab to which the wall panels are then nailed to. It is generally treated with a powerful preservative
A substantial horizontal section of timber or metal, fixed to the floor slab.