The Collaborative International Dictionary of English v.0.48:

Doorpost \Door"post`\, n.
   The jamb or sidepiece of a doorway.
   [1913 Webster]

WordNet (r) 3.0 (2006):

doorpost
    n 1: a jamb for a door [syn: doorjamb, doorpost]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "doorpost":
   French door, Samson post, archway, back door, baluster, balustrade,
   banister, barway, bulkhead, carriage entrance, cellar door,
   cellarway, door, doorjamb, doorway, front door, gate, gatepost,
   gateway, hatch, hatchway, hitching post, jamb, king post, lintel,
   milepost, mullion, porch, portal, porte cochere, post, postern,
   propylaeum, pylon, scuttle, side door, signpost, snubbing post,
   stanchion, standard, stile, storm door, threshold, tollgate, trap,
   trap door, turnpike, turnstile, upright