The Collaborative International Dictionary of English v.0.48:

Imperfect \Im*per"fect\ ([i^]m*p[~e]r"f[e^]kt), n. (Gram.)
   The imperfect tense; or the form of a verb denoting the
   imperfect tense.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Imperfect \Im*per"fect\, v. t.
   To make imperfect. [Obs.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Imperfect \Im*per"fect\, a. [L. imperfectus: pref. im- not +
   perfectus perfect: cf. F imparfait, whence OE. imparfit. See
   Perfect.]
   1. Not perfect; not complete in all its parts; wanting a
      part; deective; deficient.
      [1913 Webster]

            Something he left imperfect in the state. --Shak.
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            Why, then, your other senses grow imperfect. --Shak.
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   2. Wanting in some elementary organ that is essential to
      successful or normal activity.
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            He . . . stammered like a child, or an amazed,
            imperfect person.                     --Jer. Taylor.
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   3. Not fulfilling its design; not realizing an ideal; not
      conformed to a standard or rule; not satisfying the taste
      or conscience; esthetically or morally defective.
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            Nothing imperfect or deficient left
            Of all that he created.               --Milton.
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            Then say not man's imperfect, Heaven in fault;
            Say rather, man's as perfect as he ought. --Pope.
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   Imperfect arch, an arch of less than a semicircle; a skew
      arch.

   Imperfect cadence (Mus.), one not ending with the tonic,
      but with the dominant or some other chord; one not giving
      complete rest; a half close.

   Imperfect consonances (Mus.), chords like the third and
      sixth, whose ratios are less simple than those of the
      fifth and forth.

   Imperfect flower (Bot.), a flower wanting either stamens or
      pistils. --Gray.

   Imperfect interval (Mus.), one a semitone less than
      perfect; as, an imperfect fifth.

   Imperfect number (Math.), a number either greater or less
      than the sum of its several divisors; in the former case,
      it is called also a defective number; in the latter, an
      abundant number.

   Imperfect obligations (Law), obligations as of charity or
      gratitude, which cannot be enforced by law.

   Imperfect power (Math.), a number which can not be produced
      by taking any whole number or vulgar fraction, as a
      factor, the number of times indicated by the power; thus,
      9 is a perfect square, but an imperfect cube.

   Imperfect tense (Gram.), a tense expressing past time and
      incomplete action.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Preterimperfect \Pre`ter*im*per"fect\, a. & n. [Pref. preter- +
   imperfect.] (Gram.)
   Old name of the tense also called imperfect.
   [1913 Webster]

WordNet (r) 3.0 (2006):

imperfect
    adj 1: not perfect; defective or inadequate; "had only an
           imperfect understanding of his responsibilities";
           "imperfect mortals"; "drainage here is imperfect" [ant:
           perfect]
    2: wanting in moral strength, courage, or will; having the
       attributes of man as opposed to e.g. divine beings; "I'm only
       a fallible human"; "frail humanity" [syn: fallible,
       frail, imperfect, weak]
    n 1: a tense of verbs used in describing action that is on-going
         [syn: progressive, progressive tense, imperfect,
         imperfect tense, continuous tense]

Moby Thesaurus II by Grady Ward, 1.0:

113 Moby Thesaurus words for "imperfect":
   adulterated, aggravated, amiss, aorist, base, blemished, broken,
   burned, burst, busted, checked, chipped, cracked, crazed, cut,
   damaged, defective, deficient, deteriorated, durative, embittered,
   erroneous, exacerbated, failing, fallible, faulty, flawed,
   found wanting, future, future perfect, harmed, historical present,
   hurt, immature, impaired, imprecise, impure, in bits, in pieces,
   in shards, inaccurate, inadequate, incompetent, incomplete,
   inexact, injured, insufficient, irritated, lacerated, lacking,
   little, makeshift, maladroit, mangled, mean, mediocre, mixed,
   mutilated, not comparable, not enough, not in it, not perfect, off,
   out of it, partial, past, past perfect, patchy, perfect, petty,
   pluperfect, point tense, present, present perfect, preterit,
   progressive tense, rent, ruptured, scalded, scorched, shabby,
   shattered, short, sick, sketchy, slashed, slit, small, smashed,
   split, sprung, tense, the worse for, too little, torn, trivial,
   undeveloped, unequal to, uneven, unfinished, unperfected,
   unqualified, unsatisfactory, unsatisfying, unskillful, unsound,
   unsufficing, unthorough, wanting, weakened, worse, worse off,
   worsened



Bouvier's Law Dictionary, Revised 6th Ed (1856):

IMPERFECT. That which is incomplete.
     2. This term is applied to rights and obligations. A man has a right to
be relieved by his fellow-creatures, when in distress; but this right he
cannot enforce by law; hence it is called an imperfect right. On the other
hand, we are bound to be grateful for favors received, but we cannot be
compelled to perform such imperfect obligations. Vide Poth. Ob. arc.
Preliminaire; Vattel, Dr. des Gens, Prel. notes, Sec. 17; and Obligations.