The Collaborative International Dictionary of English v.0.48:
Fieriness \Fi"er*i*ness\, n. The quality of being fiery; heat; acrimony; irritability; as, a fieriness of temper. --Addison. [1913 Webster]WordNet (r) 3.0 (2006):
fieriness n 1: the heat or the color of fire [syn: fieriness, red heat] 2: a passionate and quick-tempered nature