The Collaborative International Dictionary of English v.0.48:

Brash \Brash\, a. [Cf. Amer. bresk, brusk, fragile, brittle.]
   Brittle, as wood or vegetables. [Colloq., U. S.] --Bartlett.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Brash \Brash\, n. [See Brash brittle.]
   1. A rash or eruption; a sudden or transient fit of sickness.
      [1913 Webster]

   2. Refuse boughs of trees; also, the clippings of hedges.
      [Prov. Eng.] --Wright.
      [1913 Webster]

   3. (Geol.) Broken and angular fragments of rocks underlying
      alluvial deposits. --Lyell.
      [1913 Webster]

   4. Broken fragments of ice. --Kane.
      [1913 Webster]

   Water brash (Med.), an affection characterized by a
      spasmodic pain or hot sensation in the stomach with a
      rising of watery liquid into the mouth; pyrosis.

   Weaning brash (Med.), a severe form of diarrhea which
      sometimes attacks children just weaned.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Brash \Brash\ (br[a^]sh), a. [Cf. Gael. bras or G. barsch harsh,
   sharp, tart, impetuous, D. barsch, Sw. & Dan. barsk.]
   Hasty in temper; impetuous. --Grose.
   [1913 Webster]

WordNet (r) 3.0 (2006):

brash
    adj 1: offensively bold; "a brash newcomer disputed the age-old
           rules for admission to the club"; "a nervy thing to say"
           [syn: brash, cheeky, nervy]

Moby Thesaurus II by Grady Ward, 1.0:

106 Moby Thesaurus words for "brash":
   abrupt, aggressive, arrogant, audacious, bearish, beastly, biggety,
   bluff, blunt, bold, brassy, brazen, brazenfaced, brusque,
   bumptious, cavalier, challenging, cheeky, churlish, chutzpadik,
   cocksure, cocky, contemptuous, crusty, curt, daring, defiant,
   defying, derisive, disdainful, disregardful, disrespectful,
   ebullient, effervescent, facy, flip, flippant, forward, fresh,
   gally, gratuitous, greatly daring, gruff, harsh, hasty, headlong,
   high-spirited, hubristic, ill-advised, impertinent, impetuous,
   impolitic, improvident, imprudent, impudent, impulsive, incautious,
   inconsiderate, indiscreet, injudicious, insolent, madcap,
   maladroit, malapert, nervy, overbold, overcareless, overconfident,
   oversure, overweening, pert, precipitate, presuming, presumptuous,
   pushful, pushing, rash, reckless, regardless of consequences,
   rough, rude, sassy, saucy, self-asserting, self-assertive, severe,
   sharp, short, smart, smart-alecky, smart-ass, snippy, surly,
   tactless, temerarious, thoughtless, truculent, uncalled-for,
   unchary, undiplomatic, untactful, unwary, uppish, uppity,
   vivacious, wise-ass