The Collaborative International Dictionary of English v.0.48:

Gumption \Gump"tion\, n. [OE. gom, gome, attention; akin to AS.
   ge['o]mian, gyman, to regard, observe, gyme care, OS. gomean
   to heed, Goth. gaumjan to see, notice.]
   [1913 Webster]
   1. Capacity; shrewdness; common sense. [Colloq.]
      [1913 Webster]

            One does not have gumption till one has been
            properly cheated.                     --Lord Lytton.
      [1913 Webster]

   2. (Paint.)
      (a) The art of preparing colors. --Sir W. Scott.
      (b) Megilp. --Fairholt.

   3. initiative; resourcefulness.
      [PJC]

   4. Courage; guts.
      [PJC]

WordNet (r) 3.0 (2006):

gumption
    n 1: sound practical judgment; "Common sense is not so common";
         "he hasn't got the sense God gave little green apples";
         "fortunately she had the good sense to run away" [syn:
         common sense, good sense, gumption, horse sense,
         sense, mother wit]
    2: fortitude and determination; "he didn't have the guts to try
       it" [syn: backbone, grit, guts, moxie, sand,
       gumption]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "gumption":
   adventuresomeness, adventurousness, aggression, aggressiveness,
   ambitiousness, astuteness, audacity, backbone, balls, boldness,
   bottle, brains, cleverness, common sense, courage, daring, drive,
   dynamism, energy, enterprise, enterprisingness, force,
   forcefulness, gameness, get-up-and-get, get-up-and-go, getup, go,
   go-ahead, go-getting, go-to-itiveness, good sense, grit, guts,
   horse sense, hustle, initiative, judgement, judgment, mettle,
   mother wit, moxie, nerve, nous, perspicaciousness, perspicacity,
   pluck, push, pushfulness, pushiness, pushingness, resourcefulness,
   sagaciousness, sagacity, shrewdness, spirit, spunk, stamina,
   up-and-comingness, venturesomeness, venturousness, vigor, wisdom