The Collaborative International Dictionary of English v.0.48:

Carboniferous \Car`bon*if"er*ous\
   (k[aum]r`b[o^]n*[i^]f"[~e]r*[u^]s), a. [Carbon + -ferous.]
   Producing or containing carbon or coal.
   [1913 Webster]

   Carboniferous age (Geol.), the age immediately following
      the Devonian, or Age of fishes, and characterized by the
      vegetation which formed the coal beds. This age embraces
      three periods, the Subcarboniferous, the Carboniferous,
      and Permian. See Age of acrogens, under Acrogen.

   Carboniferous formation (Geol.), the series of rocks
      (including sandstones, shales, limestones, and
      conglomerates, with beds of coal) which make up the strata
      of the Carboniferous age or Carboniferous period. See the
      Diagram under Geology.
      [1913 Webster]

WordNet (r) 3.0 (2006):

carboniferous
    adj 1: of or relating to the Carboniferous geologic era;
           "carboniferous rock system"
    2: relating to or consisting of or yielding carbon [syn:
       carbonaceous, carbonous, carbonic, carboniferous]
    n 1: from 345 million to 280 million years ago [syn:
         Carboniferous, Carboniferous period]