Principal English Translation: 

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), 213.

Orthographic Variants: 
cec, ced, sed, centetl
Alonso de Molina: 

ce./centetl. vno o vna.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 15r. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

CĒ pl: CĒMEH one / uno o una (M) The related bound form –CĒL has a long vowel, but CEM has a short one. The plural CĒMEH has the sense ‘one of several.’ As an example C Gives cēmé tèhuāntin ‘one of us,’ cēmé azcihuà ‘one of you women’ (Cf.85v). See CEM, -CĒL. CEHCĒ redup. CĒ CĒMEH. See CĒ.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 26.

Lockhart’s Nahuatl as Written: 

cē. one. also sometimes used much like the indefinite article in English. combining form cam-, cen-, or even cep-, cec-, etc. through assimilation. incorporated in a verb, entirely, forever, etc. has pl. cēmeh which usually still translates as one (of a larger group). īc cen, forever.

Attestations from sources in Spanish: 

cec mandado = un mandado; ced mandado = un mandado; Sed - Ome = Uno, dos; Ced - Ome - LLe = Uno, dos, tres; Sed fabor = un favor (s. XX)
Fernando Horcasitas, "La Danza de los Tecuanes," Estudios de Cultura Náhuatl 14 (1980), 239–286, ver pp. 264, 268–269, 272–273.