WordNet (r) 3.0 (2006):

gangplank
    n 1: a temporary bridge for getting on and off a vessel at
         dockside [syn: gangplank, gangboard, gangway]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "gangplank":
   Bifrost, access, adit, air lock, approach, bascule bridge,
   bateau bridge, bridge, cantilever bridge, catwalk, corridor,
   drawbridge, entrance, entranceway, entry, entryway,
   floating bridge, flyover, footbridge, gangboard, gangway, hall, in,
   ingress, inlet, intake, lift bridge, means of access, opening,
   overbridge, overcrossing, overpass, passage, passageway,
   pontoon bridge, rope bridge, span, stepping-stone, stepstone,
   suspension bridge, swing bridge, toll bridge, vestibule, viaduct,
   way, way in