The Collaborative International Dictionary of English v.0.48:

Terra \Ter"ra\, n. [It. & L. See Terrace.]
   The earth; earth.
   [1913 Webster]

   Terra alba [L., white earth] (Com.), a white amorphous
      earthy substance consisting of burnt gypsum, aluminium
      silicate (kaolin), or some similar ingredient, as
      magnesia. It is sometimes used to adulterate certain
      foods, spices, candies, paints, etc.

   Terra cotta. [It., fr. terra earth + cotta, fem. of cotto
      cooked, L. coctus, p. p. of coquere to cook. See Cook,
      n.] Baked clay; a kind of hard pottery used for statues,
      architectural decorations, figures, vases, and the like.


   Terrae filius [L., son of the earth], formerly, one
      appointed to write a satirical Latin poem at the public
      acts in the University of Oxford; -- not unlike the
      prevaricator at Cambridge, England.

   Terra firma [L.], firm or solid earth, as opposed to
      water.

   Terra Japonica. [NL.] Same as Gambier. It was formerly
      supposed to be a kind of earth from Japan.

   Terra Lemnia [L., Lemnian earth], Lemnian earth. See under
      Lemnian.

   Terra ponderosa [L., ponderous earth] (Min.), barite, or
      heavy spar.

   Terra di Sienna. See Sienna.
      [1913 Webster]

WordNet (r) 3.0 (2006):

terra firma
    n 1: the solid part of the earth's surface; "the plane turned
         away from the sea and moved back over land"; "the earth
         shook for several minutes"; "he dropped the logs on the
         ground" [syn: land, dry land, earth, ground, solid
         ground, terra firma]

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "terra firma":
   acres, alluvion, alluvium, arable land, base, basement, basis,
   bearing wall, bed, bedding, bedrock, carpet, clay, clod, cover,
   crust, deck, dirt, dry land, dust, earth, floor, floor covering,
   flooring, fond, footing, foundation, freehold, fundament,
   fundamental, glebe, grassland, ground, grounds, groundwork,
   hardpan, land, landholdings, lithosphere, marginal land, marl,
   mold, parquet, pave, pavement, paving, principle, radical,
   real estate, real property, region, regolith, riprap, rock bottom,
   rudiment, seat, sill, sod, soil, solid ground, solid rock,
   stereobate, stylobate, subaerial deposit, subsoil, substratum,
   substruction, substructure, surfacing, terra, terrain, territory,
   the country, topsoil, underbuilding, undercarriage, undergirding,
   underpinning, understruction, understructure, woodland