The Collaborative International Dictionary of English v.0.48:

Sissoo \Sis*soo"\, n. [Hind. s[imac]s?.] (Bot.)
   A leguminous tree (Dalbergia Sissoo) of the northern parts
   of India; also, the dark brown compact and durable timber
   obtained from it. It is used in shipbuilding and for gun
   carriages, railway ties, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Dalbergia sissoo
    n 1: East Indian tree whose leaves are used for fodder; yields a
         compact dark brown durable timber used in shipbuilding and
         making railroad ties [syn: sissoo, sissu, sisham,
         Dalbergia sissoo]