something invented from one's own will (see Molina)
Alonso de Molina:
ixcoyan ytlanextil. cosa inuentada de su proprio aluedrio. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 45r. col. 1. Thanks to Joe Campbell for providing the transcription.