The Collaborative International Dictionary of English v.0.48:

Tonga \Ton"ga\, n. (Med.)
   A drug useful in neuralgia, derived from a Fijian plant
   supposed to be of the aroid genus Epipremnum.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tonga \Ton"ga\, n. [Hind. t[=a]ng[=a], Skr. tama[.n]gaka.]
   A kind of light two-wheeled vehicle, usually for four
   persons, drawn by ponies or bullocks. [India]
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Tonga
    n 1: a monarchy on a Polynesian archipelago in the South
         Pacific; achieved independence from the United Kingdom in
         1970 [syn: Tonga, Kingdom of Tonga, Friendly Islands]
    2: the language of the Tongan people of south central Africa
       (Zambia and Rhodesia)