WordNet (r) 3.0 (2006):

monorail
    n 1: a railway having a single track

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "monorail":
   Amtrak, L, baggage train, branch, cable railroad, cable railway,
   choo-choo, cog railroad, cog railway, el, electric,
   electric railway, electric train, elevated, elevated railway,
   embankment, express, express train, feeder, feeder line, flier,
   freight, freight train, freighter, funicular, goods train,
   gravity-operated railway, horse railway, interurban, junction,
   light railroad, lightning express, limited, line, local, main line,
   metro, milk train, parliamentary, parliamentary train,
   passenger train, rack railway, rack-and-pinion railroad,
   rack-and-pinion railway, rail, rail line, railroad, railroad train,
   railway, rattler, roadbed, roadway, rolling stock, shuttle,
   shuttle train, sidetrack, siding, special, streamliner,
   street railway, streetcar line, subway, switchback, terminal,
   terminus, track, train, tram, tramline, trestle, trolley line,
   trunk, trunk line, tube, turnout, underground, way train