The Collaborative International Dictionary of English v.0.48:

Scrag \Scrag\, v. t. [Cf. Scrag.]
   To seize, pull, or twist the neck of; specif., to hang by the
   neck; to kill by hanging. [Colloq.]

         An enthusiastic mob will scrag me to a certainty the
         day war breaks out.                      --Pall Mall
                                                  Mag.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Scrag \Scrag\ (skr[a^]g), n. [Cf. dial. Sw. skraka a great dry
   tree, a long, lean man, Gael. sgreagach dry, shriveled,
   rocky. See Shrink, and cf. Scrog, Shrag, n.]
   1. Something thin, lean, or rough; a bony piece; especially,
      a bony neckpiece of meat; hence, humorously or in
      contempt, the neck.
      [1913 Webster]

            Lady MacScrew, who . . . serves up a scrag of mutton
            on silver.                            --Thackeray.
      [1913 Webster]

   2. A rawboned person. [Low] --Halliwell.
      [1913 Webster]

   3. A ragged, stunted tree or branch.
      [1913 Webster]

   Scrag whale (Zool.), a North Atlantic whalebone whale
      (Agaphelus gibbosus). By some it is considered the young
      of the right whale.
      [1913 Webster]

WordNet (r) 3.0 (2006):

scrag
    n 1: a person who is unusually thin and scrawny [syn: thin
         person, skin and bones, scrag] [ant: butterball,
         fat person, fatso, fatty, roly-poly]
    2: lean end of the neck
    3: the lean end of a neck of veal [syn: scrag, scrag end]
    v 1: strangle with an iron collar; "people were garrotted during
         the Inquisition in Spain" [syn: garrote, garrotte,
         garotte, scrag]
    2: wring the neck of; "The man choked his opponent" [syn:
       choke, scrag]