The Collaborative International Dictionary of English v.0.48:

Molly \Mol"ly\, n.
   A pet or colloquial name for Mary.
   [1913 Webster]

   Molly cottontail. (Zool.) See Cottontail.

   Molly Maguire (m[.a]*gw[imac]r"); pl. Molly Maguires
      (-gw[imac]rz).
   (a) A member of a secret association formed among the
       tenantry in Ireland about 1843, principally for the
       purpose of intimidating law officers and preventing the
       service of legal writs. Its members disguised themselves
       in the dress of women.
   (b) A member of a similar association of Irishmen organized
       in the anthracite coal region of Pennsylvania, about
       1854, for the purpose of intimidating employers and
       officers of the law, and for avenging themselves by
       murder on persons obnoxious to them. The society was
       broken up by criminal prosecutions in 1876.
       [1913 Webster]