The term 'thick board' can be described by two crossword solutions: PLANK (5 letters) and BEAM (4 letters). A PLANK is a long, thick, flat piece of timber or board used for flooring, roofing, or other construction purposes. A BEAM is a long, thick, strong piece of timber or metal used in the construction of buildings, bridges, and other structures. Both planks and beams are commonly used in the construction of walls, floors, roofs, and other structures.