The Collaborative International Dictionary of English v.0.48:

Big \Big\ (b[i^]g), a. [Compar. Bigger; superl. Biggest.]
   [Perh. from Celtic; cf. W. beichiog, beichiawg, pregnant,
   with child, fr. baich burden, Arm. beac'h; or cf. OE. bygly,
   Icel. biggiligr, (properly) habitable; (then) magnigicent,
   excellent, fr. OE. biggen, Icel. byggja, to dwell, build,
   akin to E. be.]
   1. Having largeness of size; of much bulk or magnitude; of
      great size; large. "He's too big to go in there." --Shak.
      [1913 Webster]

   2. Great with young; pregnant; swelling; ready to give birth
      or produce; -- often figuratively.
      [1913 Webster]

            [Day] big with the fate of Cato and of Rome.
                                                  --Addison.
      [1913 Webster]

   3. Having greatness, fullness, importance, inflation,
      distention, etc., whether in a good or a bad sense; as, a
      big heart; a big voice; big looks; to look big. As applied
      to looks, it indicates haughtiness or pride.
      [1913 Webster]

            God hath not in heaven a bigger argument. --Jer.
                                                  Taylor.
      [1913 Webster]

   Note: Big is often used in self-explaining compounds; as,
         big-boned; big-sounding; big-named; big-voiced.
         [1913 Webster]

   To talk big, to talk loudly, arrogantly, or pretentiously.
      [1913 Webster]

            I talked big to them at first.        --De Foe.
      [1913 Webster]

   Syn: Bulky; large; great; massive; gross.
        [1913 Webster] Big

The Collaborative International Dictionary of English v.0.48:

Bigger \Big"ger\, a.,
   compar. of Big.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bigger
    adj 1: large or big relative to something else [syn: bigger,
           larger]