The Collaborative International Dictionary of English v.0.48:

dacoity \da*coit"y\, n.
   The practice of gang robbery in India; robbery committed by
   dacoits.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dacoity
    n 1: robbery by a gang of armed dacoits [syn: dacoity,
         dakoity]