debilis.

Disputed. By surface analysis, the term is an adjective formed according to the model of terms such as inermis. It has been proposed that the term may derive from dēbeō (“to owe”) in the manner as habilis (“able to have”), from habeō (“to have, hold”). However, according to De Vaan, the form dēbilis is isolated within Latin and therefore likely archaic, in which case it may preserve an older i-stem form. De Vaan suggests that the term may continue either Proto-Indo-European *bel-i- or *bol-i- (“strength”), though he considers the latter pre-form more likely on the basis of Proto-Slavic *boľьjь, which also displays an o-grade. Ultimately, De Vaan connects the term with the root *bel-. Compare Sanskrit बल (bala), Russian большой (bolʹšoj), Ancient Greek βελτίων (beltíōn, “better < stronger”)