Principal English Translation: 

a count; twenty; a count of twenty (see attestations); must be preceded by a numerical indicator

Orthographic Variants: 
poali, poalli, poualli, -pōhualli
Frances Karttunen: 

-PŌHUAL-LI, a unit of twenty in the vigesimal counting system / veinte (M for CEMPŌHUAL-LI). A necessarily bound form; pl: -TIN . This is prefixed by a number which multiplies the twenty, CEMPŌHUAL-LI 'twenty,' ŌMPŌHUAL-LI 'forty' (two times twenty), etc. TLAPŌHUAL-LI means 'something countable,’ and the negated phrase AHMŌ ZAN TLAPŌHUAL-LI 'an infinite number.' See PŌHU(A).
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 201–202.

Lockhart’s Nahuatl as Written: 

cempōhualli, one twenty, i.e., twenty; ōmpōhualli, two twenties, i.e., forty, etc. patientive noun from pōhua. 230

Attestations from sources in English: 

-pohualli = preceded by a number in combining form, this means twenty times that number
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), 230.

noteutlal i poali ynic huiac auh ynic patlahuac çano ychquich (sic) 1 poalmatl = I have dry land, 20 (matl) long and also 20 matl wide (Culhuacan, 1580)
Testaments of Culhuacan (provisionally modified first edition), eds. Sarah Cline and Miguel León-Portilla, online version http://www.history.ucsb.edu/cline/testaments_of_culhuacan.pdf, 16.

Attestations from sources in Spanish: 

cen[c]a yehuecauh yyequezquipoual xihuitl = hace ya mucho tiempo, hace ya cuantas veintenas de años (ca. 1582, México)
Luis Reyes García, ¿Como te confundes? ¿Acaso no somos conquistados? Anales de Juan Bautista (Mexico: Centro de Investigaciones y Estudios Superiores en Antropología Social, Biblioteca Lorenzo Boturini Insigne y Nacional Basílica de Guadalupe, 2001), 170.