The Collaborative International Dictionary of English v.0.48:
Viscountess \Vis"count`ess\, n. [F. vicomtesse, LL. vicecomitissa.] The wife of a viscount. [1913 Webster] ViscountshipWordNet (r) 3.0 (2006):
viscountess n 1: a wife or widow of a viscount 2: a noblewoman holding the rank of viscount in her own right