The Collaborative International Dictionary of English v.0.48:

Sirdar \Sir*dar"\, n. [Hind. & Per. sard[=a]r a chief, general;
   sar the head, top + d[=a]r holding, possessing.]
   A native chief in Hindostan; a headman. --Malcom.
   [1913 Webster]

   2. In Turkey, Egypt, etc., a commander in chief, esp. the one
      commanding the Anglo-Egyptian army.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

sirdar
    n 1: an important person in India