[Corpora-List] Help from Gaelic speaker required

[Pete Whitelock]

Not really corpora related, but here goes anyway.

In Eoin Colfer's latest book, the protagonists swear loyalty by invoking
the Irish marble oath, "Brick miss must celt."

Does anyone have any idea what this looks like in the original Gaelic
before, presumably, being rendered as English words, and what it means?

Thanks

Pete Whitelock