This etymology is found only in the Additamenta to the Gudianum, twice. Its starting point is an inflected form, the future ῥήσω of "to say", a ghost-form given by the grammarian Philoxenus (and after him by Orion, Choeroboscus etc/) as the verbal basis from which are derived ῥῆμα etc. The priest gets his name from the fact that he is the one who utters the prayer. The initial [a] was probably understood as the "intensive" alpha (ἐπιτατικός), but that is not explicit in the formulation we have