Principal English Translation:
a connector linking two verbs; a connector that tells us that preceding word is a verbal preterite agentive.
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 212.
Frances Karttunen:
CĀ. This serves to bind one verb in its preterit form to a second verb. This medial –CĀ– and the final –QUI of the class of derived nouns known as preterit agentives appear to be derived from the same source. The sense of the construction is that the second verb is performed in the manner of one who is or does whatever the first verb signifies; CUALĀN(I) 'to become angry' (I)TTA 'to see something' >CUALĀNCĀITTA 'to look upon something angrily.' Preterit agentive nouns have –CĀ– in derivations; TLAHTOQUI 'ruler' (CALEH–CĀCĀHU(A) 'to turn over stewardship of a household to someone.'
Horacio Carochi / English:
-cā- = original preterit ending
Horacio Carochi, S.J., Grammar of the Mexican language with an explanation of its adverbs (1645), translated and edited with commentary by James Lockhart, UCLA Latin American Studies Volume 89 (Stanford: Stanford University Press, UCLA Latin American Center Publications, 2001), 498.
Attestations from sources in English:
When this ligature is used, the main verb will be on the right and the verb that is on the left is a modifier. For example, mimatcatlaloa = imati (to be prudent) + ca + tlaloa (to run) = to run prudently. The first m- is a reflexive indicator.
Rebecca Horn's notes from Nahuatl classes with James Lockhart at UCLA added to notes taken by Stephanie Wood in the same classes.