The Collaborative International Dictionary of English v.0.48:

assembly line \assembly line\ n.
   A line of machinery, tools, and workers on which objects to
   be manufactured are moved from one post to the next, where
   different workers perform different steps in the
   manufacturing process; called also production line. The
   objects to be manufactured usually move on a form of conveyor
   belt, which does not necessarily move only in a straight
   line, but may continue around the factory area for some
   distance.
   [PJC]

WordNet (r) 3.0 (2006):

assembly line
    n 1: mechanical system in a factory whereby an article is
         conveyed through sites at which successive operations are
         performed on it [syn: production line, assembly line,
         line]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "assembly line":
   armory, arsenal, assemblage, assembly, assembly plant,
   assembly-line production, atomic energy plant, bindery, boatyard,
   boilery, bookbindery, brewery, brickyard, cannery, creamery, dairy,
   defense plant, distillery, division of labor, dockyard, factory,
   factory belt, factory district, feeder plant, flour mill,
   industrial park, industrial zone, industrialization, main plant,
   manufactory, manufacturing plant, manufacturing quarter,
   mass production, mill, mint, modular production, munitions plant,
   oil refinery, packing house, plant, pottery, power plant,
   production line, push-button plant, refinery, sawmill, shipyard,
   standardization, subassembly plant, sugar refinery, tannery,
   volume production, winery, yard, yards