Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

Source : WordNet®

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}, {unsound}]
     [also: {unfitting}, {unfitted}]

unfit
     v : make unfit or unsuitable; "Your income disqualifies you"
         [syn: {disqualify}, {indispose}] [ant: {qualify}]
     [also: {unfitting}, {unfitted}]