Principal English Translation: 

an element used as a ligature; combines main and auxiliary verbs or nouns and relational words

Lockhart’s Nahuatl as Written: 

element used as a ligature in certain kinds of constructions, specifically between main and auxiliary verbs and between nouns and relational words.
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), 235.

Attestations from sources in English: 

For example: xochitica (through or by means of flowers); quetzaltica (through or by means of quetzal feathers). Other places one will see the -ti- ligature: tlalticpac, caltitech, tepetitlan, etc.
Michael McCafferty, Nahuat-L listserv posting, March 6, 2012.

tlamahuizoltica = through a miracle, by means of a miracle (from tlamahuizol-li, "miracle" + ti (ligature) + -ca (instrumental relational word, "with, by means of"). You could also say "ica tlamahuizolli."
John Sullivan, Nahuat-L listserv posting, March 6, 2012.