The word derives from the Irish "uaimh mhór", meaning great cave, and that etymology alone suggests this is a site shaped more by geology than by human hands, though the two are rarely entirely separate in this part of Ireland.

Killadangan sits on the southern shore of Clew Bay, a landscape of drumlins, inlets, and low hills that bears the long imprint of glacial movement. Cave sites in such areas frequently served practical purposes across different periods, offering shelter, storage, or refuge, and in some cases accumulating archaeological deposits over centuries. The name Ooghmore appears on older maps and in the placename record, which is often the most durable evidence a site retains when formal documentation remains incomplete. Placenames in Irish frequently encode a precise description of what early inhabitants found significant, and "great cave" is about as direct as such names get.