Source : Webster's Revised Unabridged Dictionary (1913)

Tupi \Tu"pi\, n.
   An Indian of the tribe from which the Tupian stock takes its
   name, dwelling, at the advent of the Portuguese, about the
   mouth of the Amazon. Also, their language, which is the basis
   of the Indian trade language of the Amazon.

Source : WordNet®

Tupi
     n 1: a member of the South American Indian people living in
          Brazil and Paraguay
     2: the language spoken by the Tupi people of Brazil and
        Paraguay