a narrow piece of land in between two seas (see Molina)
Alonso de Molina:
imonamicyan intlalli. estrechura de tierra entre dos mares. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 38r. col. 2. Thanks to Joe Campbell for providing the transcription.