Fierce

n.

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

Extremely; used to express a high degree of like or dislike.

In use

Dat fella was sumthin feirce.

Posh English

That gentleman was something quite extreme.

Same phrase, other counties