The Collaborative International Dictionary of English v.0.48:

Trestle \Tres"tle\, n. [OF. trestel, tresteay, F. tr['e]teau;
   probably from L. transtillum a little crossbeam, dim. of
   transtrum a crossbeam. Cf. Transom.] [Written also
   tressel.]
   1. A movable frame or support for anything, as scaffolding,
      consisting of three or four legs secured to a top piece,
      and forming a sort of stool or horse, used by carpenters,
      masons, and other workmen; also, a kind of framework of
      strong posts or piles, and crossbeams, for supporting a
      bridge, the track of a railway, or the like.
      [1913 Webster]

   2. The frame of a table.
      [1913 Webster]

   Trestle board, a board used by architects, draughtsmen, and
      the like, for drawing designs upon; -- so called because
      commonly supported by trestles.

   Trestle bridge. See under Bridge, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

trestle
    n 1: a supporting tower used to support a bridge
    2: sawhorses used in pairs to support a horizontal tabletop

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "trestle":
   L, branch, buck, cable railway, clotheshorse, cog railway, el,
   electric railway, elevated, elevated railway, embankment, feeder,
   feeder line, gravity-operated railway, horse, horse railway,
   junction, light railroad, line, main line, metro, monorail,
   rack railway, rack-and-pinion railway, rail, rail line, railroad,
   railway, roadbed, roadway, sawbuck, sawhorse, sidetrack, siding,
   street railway, streetcar line, subway, switchback, terminal,
   terminus, track, tram, tramline, trestle and table, trestle board,
   trestle table, trestlework, trestling, trolley line, trunk,
   trunk line, tube, turnout, underground, workhorse