Fierce

n.

Heard in Cavan, Cork, Kilkenny, Donegal, Mayo, Offaly, Roscommon, Galway, Meath, Waterford and Kildare

An intensifier denoting extreme degree or magnitude.

In use

Yer wan has a fierce arse on her, and it's fierce cold out here!

Posh English

That young lady has a very fine posterior indeed, and it is terribly chilly out here.

Same phrase, other counties