Nheterõîa

Uncertain. According to Frederico Edelweiss, from nhe- (reflexive prefix) +‎ *terõ (“twisted, crooked, sinuous”) +‎ îá (particle of habit, of customary or persistent trait), literally “the [bay that is] very winding”, although the îá would have to become unstressed, and he does not provide other examples of the particle in question acting in a similar way. Edelweiss supports this hypothesis through José de Anchieta’s poem De gestis Mendi de Saa, where the port of Rio de Janeiro is twice referred to as the “winding port”. The word *terõ is not attested in Old Tupi, but it is in Classical Guaraní, in the vocabulary of Antonio Ruiz de Montoya.

Eduardo de Almeida Navarro himself did not dare to provide an etymology for the toponym in his dictionary.

Compare Nheterõaíba, the name of a village in Cabo Frio.

Nheterõîa

1. A bay in São Vicente Captaincy, equivalent to modern-day Guanabara Bay, Rio de Janeiro, Brazil, and its surrounding regions, namely modern-day Niterói and Rio de Janeiro
   • c. 1583, Joseph of Anchieta, “Na feſta de .ſ. L^ço [At the Saint Lawrence Festival]” (chapter XLIV), in [livrinho de variaſ poeziaſ] [Booklet of various poems], Niterói, page 63, lines 142–151; republished as Maria de Lourdes de Paula Martins, compiler, Poesias, São Paulo, 1956, page 691:

     Maene, Tupinãba / Paraguaçupe ndaroera, / ytupã ocibae puera / opacatu yamomba / nitibetei çembiroera // Yaupa Moçupiroca, / Yequej, guatapitiba, / Nheterõya, Paraiba / Guayayo, Carijo oca / Pacucaya, Araçatiba.

     [Ma'ẽne, tupinambá / Paragûasupendarûera, / i tupãokyba'epûera, / opakatu îamombá. / N'i tybetéî sembyrûera. // Îa'upá Mosupyroka, / Îekeí, Gûatapytyba, / Nheterõîa, Paraíba, / Gûaîaîó, Kariîooka, / Pakukaîa, Arasatyba.]

     Look, the Tupinambás who were in Paraguaçu and had their churches, we destroyed them all. Not even their remains are left. We devoured all the Moçupiroca, Jequeí, Guatapitiba, Niterói, Paraíba, Guajajó, Carioca, Pacucaia, Araçatiba.

• → Portuguese: Niterói

• anonymous author (1622), “Rio de Janeiro”, in Vocabulario na lingoa Braſilica (overall work in Portuguese), Piratininga; republished as Carlos Drummond, editor, Vocabulário na Língua Brasílica, 2nd edition, volume 2, São Paulo: USP, 1953, page 106: “Nheteroya”