Some dictionaries give it as ‘jocose’ but it doesn’t really do it justice as it combines elements of blasphemy and tempting fate or providence.

A ‘joke’ about not wishing to risk one’s life at the hands of a relative’s driving [or indeed any kind of mucking about while driving] might result in the admonishment ‘Paid a cellwair’.

Tranlated as “Don’t, er, ‘cellwair’..”