huel icuac.

Headword: 
huel icuac.
Principal English Translation: 

right when; right then, at that moment (see Molina)

Orthographic Variants: 
huel iquac
Alonso de Molina: 

uel iquac. ala sazon, entonces o al momento. aduerbio.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 156r. col. 2. Thanks to Joe Campbell for providing the transcription.

Attestations from sources in English: 

The huel is an intensifier. Icuac (or iquac) says "when."
Rebecca Horn's notes from classes in Nahuatl with James Lockhart. Some of her note cards are harvested here by Stephanie Wood.