The Collaborative International Dictionary of English v.0.48:

Tripoli \Trip"o*li\, n. (Min.)
   An earthy substance originally brought from Tripoli, used in
   polishing stones and metals. It consists almost wholly of the
   siliceous shells of diatoms.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tripoli
    n 1: a weathered and decomposed siliceous limestone; in powdered
         form it is used in polishing [syn: rottenstone,
         tripoli]
    2: the capital and chief port and largest city of Libya; in
       northwestern Libya on the Mediterranean Sea; founded by the
       Phoenicians in the 7th century BC [syn: Tripoli, Tarabulus
       Al-Gharb, capital of Libya]
    3: a port city and commercial center in northwestern Lebanon on
       the Mediterranean Sea [syn: Tarabulus, Tripoli,
       Tarabulus Ash-Sham, Trablous]