- diag
- deug, diag-teen, e.g., cóig-deug, fif-teen, Irish déag, Old Irish déc, deac, Welsh deng, ten (?). The exact relationship of deug to deich is difficult to decide. The other Indo-European languages, as a rule, make 13 to 19 by combining the unit numeral with 10, as German drei-zehn, Anglo-Saxon ðríténe, Latin tridecim. *dvei-penge (St.).
Etymological dictionary of the Gaelic language. Alexander Gairm Publications. 1982.