The Collaborative International Dictionary of English v.0.48:

Tupian \Tu"pi*an\, a.
   Designating, or pertaining to, a linguistic stock of South
   American Indians comprising the most important Brazilian
   tribes. Agriculture, pottery, and stone working were
   practiced by them at the time of the conquest. The Tupi and
   the Guarani were originally the most powerful of the stock,
   which is hence also called Tupi-Guaranian.
   [Webster 1913 Suppl.]