Source : Webster's Revised Unabridged Dictionary (1913)

Halidom \Hal"i*dom\, n. [AS. h[=a]ligd?m holiness, sacrament,
   sanctuary, relics; h[=a]lig holy + -d?m, E. -dom. See
   {Holy}.]
   1. Holiness; sanctity; sacred oath; sacred things; sanctuary;
      -- used chiefly in oaths. [Archaic]

            So God me help and halidom.           --Piers
                                                  Plowman.

            By my halidom, I was fast asleep.     --Shak.

   2. Holy doom; the Last Day. [R.] --Shipley.