The Collaborative International Dictionary of English v.0.48:

Slapdash \Slap"dash`\, v. t.
   To apply, or apply something to, in a hasty, careless, or
   rough manner; to roughcast; as, to slapdash mortar or paint
   on a wall, or to slapdash a wall. [Colloq.] --Halliwell.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Slapdash \Slap"dash`\, adv. [Slap + dash.]
   1. In a bold, careless manner; at random. [Colloq.]
      [1913 Webster]

   2. With a slap; all at once; slap. [Colloq.] --Prior.
      [1913 Webster]

WordNet (r) 3.0 (2006):

slapdash
    adv 1: in a careless or reckless manner; "the shelves were put
           up slapdash" [syn: slapdash, slam-bang]
    2: directly; "he ran bang into the pole"; "ran slap into her"
       [syn: bang, slap, slapdash, smack, bolt]
    adj 1: marked by great carelessness; "a most haphazard system of
           record keeping"; "slapdash work"; "slipshod spelling";
           "sloppy workmanship" [syn: haphazard, slapdash,
           slipshod, sloppy]

Moby Thesaurus II by Grady Ward, 1.0:

140 Moby Thesaurus words for "slapdash":
   a corps perdu, accident-prone, aimless, airily, amain, any old way,
   any which way, anyhow, apace, at once, breakneck, bunglingly,
   by forced marches, careless, carelessly, casually, clumsily,
   cursorily, cursory, designless, desperate, desperately, desultory,
   devil-may-care, disregardfully, expeditious, expeditiously,
   festinate, feverish, feverishly, flying, forgetfully, furious,
   furiously, hand over fist, haphazard, haphazardly, happen what may,
   harum-scarum, hastily, hasty, head over heels, headfirst,
   headforemost, headlong, heedlessly, heels over head,
   helter-skelter, hit and miss, hit or miss, hit-or-miss,
   holus-bolus, hotfoot, hotheaded, hotheadedly, hurried, hurriedly,
   hurry-scurry, immediate, immediately, impetuous, impetuously,
   in passing, inattentively, inconsiderately, indiscriminate,
   instant, instantly, irregular, last-minute, like crazy, like mad,
   mad, madly, messily, messy, offhand, offhandedly, on the run,
   on the spot, once over lightly, overeager, overeagerly,
   overenthusiastic, overenthusiastically, overzealous, overzealously,
   passing, pell-mell, perfunctorily, precipitant, precipitantly,
   precipitate, precipitately, precipitous, precipitously,
   promiscuous, promiscuously, prompt, promptly, quick, quickly,
   ramble-scramble, reckless, recklessly, regardlessly, slam-bang,
   slap-bang, sloppily, sloppy, slovenly, snap, speedily, speedy,
   spot, superficial, superficially, swift, swiftly, tactlessly,
   thoughtlessly, unguardedly, unheedfully, unheedingly, unmindfully,
   unsolicitously, unthinkingly, unthorough, untidy, unvigilantly,
   unwarily, urgent, wanton, wantonly, wild, wildly, with a rush,
   with all haste, with dispatch, with haste