Thank you, Pat. That is very fascinating. As it happens, it is actually in the Killorglin area, where I find the name.
Any clue, as to what might be its significance?
Also, in the Killorglin area, I have found the name Malachi which appears in the parish records, seemingly in order to differentiate people who have the name O'Brien. I've supposed it might refer to people who shared a common grandfather named Malachi, but that is pure guesswork. One man who knew this circle had the name Malachi O'Brien. I've thought that he might be named after the theoretical grandfather from whom the name derives.
I've also noticed one or too other strange name substitutions in Killorglin, like Moana or Moany, seemingly for someone named Murphy.
I've read that in the Blasket Islands, different families with the same surname had a second name to help differentiate each family, which was derived from an illustrious ancestor.