Source : Webster's Revised Unabridged Dictionary (1913)

King-post \King"-post`\, n. (Carp.)
   A member of a common form of truss, as a roof truss. It is
   strictly a tie, intended to prevent the sagging of the
   tiebeam in the middle. If there are struts, supporting the
   main rafters, they often bear upon the foot of the king-post.
   Called also {crown-post}.