achcolli.

ACHCŌL-LI great-grandfather, ancestor / bisabuelo (M for achtontli, which is in apposition with ACHCŌL-LI in B)[(4)Bf.6v,7r,8r,IIV,(3)Xp.32] All the attestations are possessed plurals with reduplication of the CŌL element: COHCŌL. Two attestations have the first element with a specifically marked short vowel, two with a specifically marked long vowel. In the paired form ACHTŌN-TLI, Bf.6v, the vowel of the first element is specifically marked short. This is inconsistent with the first element of ĀCHCĀUH-TLI ´elder brother,´which is without exception marked long, but it agrees with ACHTO ´first.´ X appears to have reanalyzed the plural as a singular and dropped ACH. See CŌL-LI.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 2.

Update from the list of errata: In the entry for achco:lli, the statement “All attestations are possessed plurals with reduplication of the co:l element” is probably incorrect. The form “achcohcoltzin” appears once in the Bancroft dialogues as singular, so the “coh” probably is not plural reduplication.