This etymology implies a phonetic manipulation, the loss of the [r]. The scholiast may have had in mind the fact that the Doric and Aeolic form matching Ionic-Attic πρός is ποτί, which has no [r]. The etymology starts from the participle of the verb, προσίων, hence *ποσίων with dropping of the [r], which happens to be the genitive plural of "husband" (although that is not explicit in the formulation). This is a functional etymology: the husband is defined as the one who approaches his wife for sexual union