the black part of the eye (see Molina)
totlilticauh. lo negro del ojo. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 150r. col. 2. Thanks to Joe Campbell for providing the transcription.
Is this a possessive form of a noun, tlilticatl?