O'Neill uses 'Cliffs of Moher' in DMI (#121). The version in W&S has the configuration most old players used to have: the low part first, a practice that has become reversed and probably helps to evoke the scaling heights of the Cliffs.

O'Neill doesn't supply an explanation for the title but I image he had no name for the tune (or failed to connect it to the tune in his earlier collection, which was given in G although obviously the same melody) and named it for the last of a batch of material to transcribe for the day. I don't think there's much more to it than that.