The Collaborative International Dictionary of English v.0.48:

Muniment \Mu"ni*ment\, n. [L. munimentum, fr. munire to fortify.
   See Munition.]
   1. The act of supporting or defending. [Obs.]
      [1913 Webster]

   2. That which supports or defends; stronghold; place or means
      of defense; munition; assistance. "Other muniments and
      petty helps." --Shak.
      [1913 Webster]

   3. (Law) A record; the evidences or writings whereby a man is
      enabled to defend the title to his estate; title deeds and
      papers. --Blount.
      [1913 Webster]

   Muniment room or Muniment house, that room in a
      cathedral, castle, or other public building, which is used
      for keeping the records, charters, seals, deeds, and the
      like. --Gwilt.
      [1913 Webster]

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

MUNIMENTS. The instruments of writing and written evidences which the owner
of lands, possessions, or inheritances has, by which he is enabled to defend
the title of his estate. Termes de la Ley, h.t.; 3 Inst. 170.