The Collaborative International Dictionary of English v.0.48:

Unfit \Un*fit"\, v. t. [1st pref. un- + fit.]
   To make unsuitable or incompetent; to deprive of the
   strength, skill, or proper qualities for anything; to
   disable; to incapacitate; to disqualify; as, sickness unfits
   a man for labor; sin unfits us for the society of holy
   beings.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Unfit \Un*fit"\, a. [Pref. un- + fit.]
   Not fit; unsuitable. -- Un*fit"ly, adv. -- Un*fit"ness,
   n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unfit
    adj 1: below the required standards for a purpose; "an unfit
           parent"; "unfit for human consumption" [ant: fit]
    2: not in good physical or mental condition; out of condition;
       "fat and very unfit"; "certified as unfit for army service";
       "drunk and unfit for service" [ant: fit]
    3: physically unsound or diseased; "has a bad back"; "a bad
       heart"; "bad teeth"; "an unsound limb"; "unsound teeth" [syn:
       bad, unfit, unsound]
    v 1: make unfit or unsuitable; "Your income disqualifies you"
         [syn: disqualify, unfit, indispose] [ant: dispose,
         qualify]

Moby Thesaurus II by Grady Ward, 1.0:

155 Moby Thesaurus words for "unfit":
   aberrant, abnormal, abominable, atrocious, bad, criminal,
   delinquent, deviant, discordant, disgraceful, disqualified, evil,
   functionless, futile, hardly the thing, ignominious, ill-adapted,
   ill-advised, ill-assorted, ill-chosen, ill-considered,
   ill-equipped, ill-fitted, ill-furnished, ill-matched, ill-provided,
   ill-qualified, ill-seasoned, ill-sorted, ill-suited, ill-timed,
   illegal, impolitic, improper, in disrepair, inadequate,
   inadmissible, inadvisable, inapplicable, inapposite, inappropriate,
   inapt, inauspicious, incapable, incapable of, incompatible,
   incompetent, incongruous, inconvenient, incorrect, indecorous,
   ineffective, ineffectual, inefficient, inept, inexpedient,
   infamous, infelicitous, inferior, inharmonious, inoperable,
   inoperative, inopportune, intempestive, intrusive, irrelevant,
   late, mal a propos, maladjusted, malapropos, misjoined, mismatched,
   mismated, misplaced, mistimed, nonfunctional, nonutilitarian,
   not done, not equal to, not the thing, not up to, off base,
   off-base, off-color, otiose, out of, out of character,
   out of joint, out of keeping, out of line, out of order,
   out of phase, out of place, out of proportion, out of season,
   out of time, out of tune, out of whack, out-of-line, premature,
   sacrilegious, scandalous, shameful, shameless, sinful, terrible,
   too late, too soon, unable, unable to, unadapted, unadjusted,
   unapt, unarmed, unbecoming, unbefitting, unconducive, uncongenial,
   undesirable, undue, unemployable, unendowed, unequipped,
   unfavorable, unfitted, unfitting, unfortunate, ungifted, unhandy,
   unhappy, unhelpful, unlawful, unlucky, unmeet, unprofitable,
   unpropitious, unprovided, unqualified, unready, unrighteous,
   unripe, unseasonable, unseemly, unskillful, unsuitable, unsuited,
   untalented, untimely, untoward, unusable, unwise, unworkable,
   wicked, wrong, wrongful