Principal English Translation: 

tlahmati = to jest, to practice trickery and deception; or, to be quick-witted (see Karttunen and Molina)
tlamati = to know something; to know magic
(It is not clear that these are separate words. To "know something" and "to know magic" are both definitions--among others--that are given for tlamati in the Gran Diccionario Nahuatl. The suggestions of deception, trickery, and magic may be evidence of a European friars' filter entering into some of the translations.)

Orthographic Variants: 
Alonso de Molina: 

tlamati. ni. (pret. onitlamat.) embaucar a otro el hechizero. &c.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 126r. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

TLAHMAT(I) pret: TLAHMAT to jest, to practice trickery and deception, to be quick-witted / embaucar a otro el hechicero (M), travesar (M) [(2)Cf.128v]. Although IHMAT(I) retains the initial I after reflexive prefixes, it loses it with fused TLA-. This contrasts with TLAMAT(I) ‘to know something’ Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 261.

Attestations from sources in English: 

See the Nahuatl hieroglyphs for the name Tlamauh (often glossed as Tlamao) as they appear in the Visual Lexicon. The use of the stellar or starry eye suggests a special type of knowledge that is gained through seeing--along the lines suggested by Marc Thouvenot: "Mientras que imati se relaciona con un conocimiento empírico dado po la experiencia a través del ojo, mati hace referencia a un saber interno, abstracto, dado por la capacidad de pensar."
Marc Thouvenot, "Imágenes y escritura entre los Nahuas del inicio del XVI," Estudios de Cultura Náhuatl 41 (2010), 182.