The Collaborative International Dictionary of English v.0.48:

Dhow \Dhow\, n. [Ar. d[=a]o?]
   A coasting vessel of Arabia, East Africa, and the Indian
   Ocean. It has generally but one mast and a lateen sail. [Also
   written dow.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

dhow
    n 1: a lateen-rigged sailing vessel used by Arabs