a hen that is sitting on its eggs; the woman that is raising chickens; or, the man that rules or governs (see Molina)
Alonso de Molina:
tlapacho. gallina que esta sobre los hueuos, o la que cria pollos, o el que rige y gouierna. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 130v. col. 1. Thanks to Joe Campbell for providing the transcription.