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]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "scrag":
   KO, and quarter, call off, cancel, complete, delete, dispose of,
   draw, drop the curtain, end off, expunge, extinguish, finalize,
   finish, fold up, get it over, get over with, get through with,
   gibbet, give the quietus, hang, kayo, kibosh, kill, knock out,
   liquidate, lynch, neck, noose, perfect, polish off, put paid to,
   rackabones, shoot down, stack of bones, stretch, string up, turn,
   wipe out, zap