WordNet (r) 3.0 (2006):

imprecise
    adj 1: not precise; "imprecise astronomical observations"; "the
           terms he used were imprecise and emotional" [ant:
           precise]

Moby Thesaurus II by Grady Ward, 1.0:

118 Moby Thesaurus words for "imprecise":
   adulterated, aleatoric, aleatory, ambiguous, amorphous,
   approximate, approximative, barbarous, blemished, blobby, blurred,
   blurry, broad, careless, chance, chancy, chaotic, cloudy, confused,
   damaged, defective, deficient, disordered, easy, easygoing,
   erroneous, fallible, faulty, foggy, found wanting, fuzzy, general,
   hazy, hit-or-miss, ill-defined, immature, impaired, imperfect,
   impotent, improper, impure, inaccurate, inadequate, inchoate,
   incoherent, incomplete, incorrect, indecisive, indefinable,
   indefinite, indeterminable, indeterminate, indifferent, indistinct,
   inexact, inexplicit, infelicitous, lacking, lax, lenient, loose,
   makeshift, mediocre, mixed, negligent, nonspecific, not perfect,
   obscure, off, orderless, out of line, out of plumb, out of square,
   out of true, overindulgent, overpermissive, partial, patchy,
   permissive, random, relaxed, remiss, shadowed forth, shadowy,
   shapeless, short, sketchy, slack, slipshod, sloppy, slovenly, soft,
   solecistic, stochastic, sweeping, unclear, undefined, undestined,
   undetermined, undeveloped, uneven, unfactual, unfinished,
   ungrammatic, unperfected, unplain, unprecise, unrestrained,
   unrigorous, unsound, unspecified, unthorough, vague, veiled,
   wanting, weak, woolly, wrong