Source : Webster's Revised Unabridged Dictionary (1913)

Infirm \In*firm"\, v. t. [L. infirmare : cf. F. infirmer.]
   To weaken; to enfeeble. [Obs.] --Sir W. Raleigh.

Infirm \In*firm"\ ([i^]n*f[~e]rm"), a. [L. infirmus: cf. F.
   infirme. See {In-} not, and {Firm}, a.]
   1. Not firm or sound; weak; feeble; as, an infirm body; an
      infirm constitution.

            A poor, infirm, weak, and despised old man. --Shak.

   2. Weak of mind or will; irresolute; vacillating. ``An infirm
      judgment.'' --Burke.

            Infirm of purpose!                    --Shak.

   3. Not solid or stable; insecure; precarious.

            He who fixes on false principles treads or infirm
            ground.                               --South.

   Syn: Debilitated; sickly; feeble; decrepit; weak; enfeebled;
        irresolute; vacillating; imbecile.

Source : WordNet®

infirm
     adj 1: confined to bed (by illness) [syn: {bedfast}, {bedridden}, {bedrid},
             {sick-abed}]
     2: lacking physical strength or vitality; "a feeble old woman";
        "her body looked sapless" [syn: {decrepit}, {debile}, {feeble},
         {sapless}, {weak}, {weakly}]
     3: lacking firmness of will or character or purpose; "infirm of
        purpose; give me the daggers" - Shakespeare
     4: weak and feeble; "I'm feeling seedy today" [syn: {debilitated},
         {enfeebled}, {seedy}]