borrowed from Portuguese aí "sloth (the animal)," borrowed from Tupi aɨ́
Note: The Tupi form is based on that given by Aryon Rodrigues in "Contribuição para a etimologia dos brasileirismos," Revista Portuguesa de Filologia, vol. 9, I-II (1958-59), p. 14. The word can be found with various spellings in a number of early sources: André Thevet, Les singularitez de la France Antarctique, 1558 (Haü, Haüthi); Jean de Léry, Histoire d'un voyage faict en la terre du Bresil, 1578 (Hay); letter of José de Anchieta, 1560, in Serafim Leite, editor, Cartas dos primeiros Jesuítas do Brasil, vol. 3 [1958], p. 222, cited in Antônio Geraldo da Cunha, Dicionário histórico das palavras portuguesas de origem tupi, São Paulo, 1978 ("Est aliud animal quod Indi aig, nos propter nimiam tarditatem pigritiam dicimus" — "There is another animal that the Indians call aig, that we call on account of its excessive slowness the sloth"); Gabriel Soares de Sousa, Tratado descritivo do Brasil, 1587 (ahy).