PLANK, noun A broad piece of sawed timber, differing from a board only in being thicker. In America, broad pieces of sawed timber which are not more than an inch or an inch and a quarter thick, are called boards; like pieces from an inch and a half to three or four inches thick, are called planks. Sometimes pieces more than four inches thick are called planks. PLANK, verb transitive To cover or lay with planks; as, to plank a floor or a ship.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI