Principal English Translation: 

with, by means of, from, through (instrumental particle)

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.

Horacio Carochi / English: 

-ca = instrumental relational word
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), 82–85, 498.

Attestations from sources in English: 

noca = with me, with my help, from me, through me, at me
moca = (ditto) you
ica = (ditto) him/her
toca = (ditto) us
amoca = (ditto) you all
inca = (ditto) them
teca = (ditto) someone

With or through flowers: xochitica (includes the ligature -ti-); with or through quetzal feathers: quetzaltica (also with the ligature -ti-).

The ligature is not used in the examples above (noca, moca, etc.), and it is not used with the indefinite pronouns te- and tla-.
Michael McCafferty, Nahuat-L listserv posting, March 6, 2012.