Principal English Translation:
to melt; for something liquid to end up strange; or, to become very happy (see Molina)
Alonso de Molina:
atia. n. (pret. onatix.) derretirse o regalarse algo, o pararse ralo lo espesso, o alegrarse mucho.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 7v. col. 2. Thanks to Joe Campbell for providing the transcription.
Attestations from sources in English:
atia = it becomes loose (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 10 -- The People, No. 14, Part 11, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1961), 97.
Attestations from sources in Spanish:
atia = fundirse; atic = fundido
Rémi Siméon, Diccionario de la lengua náhuatl o mexicana (Mexico: Siglo XXI, 1988), xli.