fierceness

Concise Oxford English Dictionary © 2008 Oxford University Press:
fierce/fɪəs/

▶adjective (fiercer, fiercest) violent or aggressive; ferocious.

■ intense: fierce opposition.

■ (of a mechanism) having a powerful abruptness of action.

– phrases
something fierce N. Amer. informal to a great extent.

– derivatives
fiercely adverb,
fierceness noun.

– origin ME: from OFr. fiers ‘fierce, brave’, from L. ferus ‘untamed’.