The Collaborative International Dictionary of English v.0.48:

Rash \Rash\ (r[a^]sh), v. t. [For arace.]
   1. To pull off or pluck violently. [Obs.]
      [1913 Webster]

   2. To slash; to hack; to cut; to slice. [Obs.]
      [1913 Webster]

            Rashing off helms and riving plates asunder.
                                                  --Spenser.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rash \Rash\, n. [OF. rasche an eruption, scurf, F. rache; fr.
   (assumed) LL. rasicare to scratch, fr. L. radere, rasum, to
   scrape, scratch, shave. See Rase, and cf. Rascal.] (Med.)
   A fine eruption or efflorescence on the body, with little or
   no elevation.
   [1913 Webster]

   Canker rash. See in the Vocabulary.

   Nettle rash. See Urticaria.

   Rose rash. See Roseola.

   Tooth rash. See Red-gum.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rash \Rash\, n. [Cf. F. ras short-nap cloth, It. & Sp. raso
   satin (cf. Rase); or cf. It. rascia serge, G. rasch,
   probably fr. Arras in France (cf. Arras).]
   An inferior kind of silk, or mixture of silk and worsted.
   [Obs.] --Donne.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rash \Rash\, a. [Compar. Rasher (-[~e]r); superl. Rashest.]
   [Probably of Scand. origin; cf. Dan. & Sw. rask quick, brisk,
   rash, Icel. r["o]skr vigorous, brave, akin to D. & G. rasch
   quick, of uncertain origin.]
   1. Sudden in action; quick; hasty. [Obs.] "Strong as aconitum
      or rash gunpowder." --Shak.
      [1913 Webster]

   2. Requiring sudden action; pressing; urgent. [Obs.]
      [1913 Webster]

            I scarce have leisure to salute you,
            My matter is so rash.                 --Shak.
      [1913 Webster]

   3. Esp., overhasty in counsel or action; precipitate;
      resolving or entering on a project or measure without due
      deliberation and caution; opposed to prudent; said of
      persons; as, a rash statesman or commander.
      [1913 Webster]

   4. Uttered or undertaken with too much haste or too little
      reflection; as, rash words; rash measures.
      [1913 Webster]

   5. So dry as to fall out of the ear with handling, as corn.
      [Prov. Eng.] --Grose.
      [1913 Webster]

   Syn: Precipitate; headlong; headstrong; foolhardy; hasty;
        indiscreet; heedless; thoughtless; incautious; careless;
        inconsiderate; unwary.

   Usage: Rash, Adventurous, Foolhardy. A man is
          adventurous who incurs risk or hazard from a love of
          the arduous and the bold. A man is rash who does it
          from the mere impulse of his feelings, without
          counting the cost. A man is foolhardy who throws
          himself into danger in disregard or defiance of the
          consequences.
          [1913 Webster]

                Was never known a more adventurous knight.
                                                  --Dryden.
          [1913 Webster]

                Her rash hand in evil hour
                Forth reaching to the fruit, she plucked, she
                eat.                              --Milton.
          [1913 Webster]

                If any yet be so foolhardy
                To expose themselves to vain jeopardy;
                If they come wounded off, and lame,
                No honor's got by such a maim.    --Hudibras.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rash \Rash\ (r[a^]sh), v. t.
   To prepare with haste. [Obs.] --Foxe.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rash
    adj 1: imprudently incurring risk; "do something rash that he
           will forever repent"- George Meredith
    2: marked by defiant disregard for danger or consequences;
       "foolhardy enough to try to seize the gun from the hijacker";
       "became the fiercest and most reckless of
       partisans"-Macaulay; "a reckless driver"; "a rash attempt to
       climb Mount Everest" [syn: foolhardy, heady, rash,
       reckless]
    n 1: any red eruption of the skin [syn: rash, roseola,
         efflorescence, skin rash]
    2: a series of unexpected and unpleasant occurrences; "a rash of
       bank robberies"; "a blizzard of lawsuits" [syn: rash,
       blizzard]

Moby Thesaurus II by Grady Ward, 1.0:

165 Moby Thesaurus words for "rash":
   abrupt, abscess, adventuresome, adventurous, ague, anemia,
   ankylosis, anoxia, apnea, asphyxiation, asthma, ataxia, atrophy,
   audacious, backache, bleeding, blennorhea, bold, brash, brazen,
   brazenfaced, breaking out, breakneck, breathless, cachexia,
   cachexy, careless, chill, chills, colic, constipation, convulsion,
   coughing, cyanosis, daredevil, daring, dashing, deluge, dermatitis,
   devil-may-care, diaper rash, diarrhea, dizziness, dropsy,
   drug rash, dysentery, dyspepsia, dyspnea, eczema, edema,
   efflorescence, emaciation, epidemic, eruption, fainting, fatigue,
   fever, fibrillation, flood, flux, foolhardy, foolish, growth,
   hasty, headlong, heat rash, heedless, hemorrhage,
   high blood pressure, hives, hotheaded, hubristic, hydrops,
   hypertension, hypotension, icterus, ill-advised, ill-considered,
   impatient, impetuous, improvident, imprudent, impudent, impulsive,
   incautious, incogitant, inconsiderate, indigestion, indiscreet,
   inflammation, injudicious, insolent, insomnia, itching, jaundice,
   labored breathing, lots, low blood pressure, lumbago, madcap,
   marasmus, multitude, nasal discharge, nausea, necrosis,
   nettle rash, numbers, outbreak, overbold, overcareless,
   overconfident, overhasty, oversure, overweening, pain, panting,
   papular rash, paralysis, plague, precipitant, precipitate,
   precipitous, prickly heat, profusion, pruritus, quantity, quick,
   quixotic, reckless, redness, rheum, rupia, sclerosis, seizure,
   series, shock, silly, skin eruption, sneezing, sore, spasm, spate,
   succession, sudden, tabes, tachycardia, temerarious, thoughtless,
   tumor, unadvised, unchary, unconsidered, unthinking, unwary,
   unwise, upset stomach, urticaria, vaccine rash, venturesome,
   venturous, vertigo, vomiting, wasting, wave, wild



The Devil's Dictionary (1881-1906):

RASH, adj.  Insensible to the value of our advice.

    "Now lay your bet with mine, nor let
        These gamblers take your cash."
    "Nay, this child makes no bet."  "Great snakes!
        How can you be so rash?"
                                                        Bootle P. Gish