éifeachd Definitions (by source) Show all An Teagasg Críosdaidhe substance, 1722, importance, 3026; aid. éifeachdach 1961, 3021. An Teagasg Críosdaidhe. Author: Bonabhentura Ó hEodhasa, O.F.M.. Editor: Fearghal Mac Raghnaill, O.F.M.