Merriam-Webster Collegiate Dictionary - gantry

 noun  (plural gantries)  Etymology: Middle English ganter, gauntree, from Anglo-French *ganter, from Old French dialect (Artois) gantier, from Latin cantherius horse of poor quality, rafter, trellis  Date: 15th century  1. a frame for supporting barrels  2. a frame structure raised on side supports so as to span over or around something: as  a. a platform made to carry a traveling crane and supported by towers or side frames running on parallel tracks; also a movable structure with platforms at different levels used for erecting and servicing rockets before launching  b. a structure spanning several railroad tracks and displaying signals for each