The Collaborative International Dictionary of English v.0.48:

Maim \Maim\, n. [Written in law language maihem, and
   mayhem.] [OF. mehaing. See Maim, v.]
   1. The privation of the use of a limb or member of the body,
      by which one is rendered less able to defend himself or to
      annoy his adversary.
      [1913 Webster]

   2. The privation of any necessary part; a crippling;
      mutilation; injury; deprivation of something essential.
      See Mayhem.
      [1913 Webster]

            Surely there is more cause to fear lest the want
            there of be a maim than the use of it a blemish.
                                                  --Hooker.
      [1913 Webster]

            A noble author esteems it to be a maim in history
            that the acts of Parliament should not be recited.
                                                  --Hayward.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

mayhem \may"hem\, n. [The same as maim. See Maim.]
   1. (Law) The maiming of a person by depriving him of the use
      of any of his members which are necessary for defense or
      protection. See Maim.
      [1913 Webster]

   2. Violent disorder, especially such as causes serious harm
      to persons or damage to property.
      [PJC]

WordNet (r) 3.0 (2006):

mayhem
    n 1: the willful and unlawful crippling or mutilation of another
         person
    2: violent and needless disturbance [syn: havoc, mayhem]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "mayhem":
   bankruptcy, breakage, breakdown, chaos, collapse, commotion,
   confusion, crack-up, cripple, crippling, damage, destruction,
   detriment, devastation, dilapidation, disablement, dismember,
   disorder, disrepair, encroachment, fracas, harm, havoc, hobbling,
   hurt, hurting, impairment, incapacitation, infringement, injury,
   inroad, loss, maiming, mischief, mutilate, mutilation, ruination,
   ruinousness, sabotage, scathe, sickening, spoiling, violence,
   weakening



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

MAYHEM, crimes. The act of unlawfully and violently depriving another of the
use of such of his members as may render him less able in fighting either to
defend himself or annoy his adversary; and therefore the cutting or
disabling, or weakening a man's hand or finger, or striking out his eye or
foretooth, or depriving him of those parts the loss of which abates his
courage, are held to be mayhems. But cutting off the ear or nose or the
like, are not held to be mayhems at common law. 4 Bl. Com. 205.
     2. These and other severe personal injuries are punished by the
Coventry act, (q.v.) which has been re-enacted in several of the states;
Ryan's Med. Jurispr. 191, Phil. ed. 1832; and by congress. Vide act of
April 30, 1790, s. 13, 1 Story's Laws U. S. 85; act of March 3, 1825, s. 22,
3 Story's L. U. S. 2006.