duchess

Concise Oxford English Dictionary © 2008 Oxford University Press:
duchess/ˈdʌtʃəs/

▶noun

• 1 the wife or widow of a duke.

  ■ a woman holding a rank equivalent to duke in her own right.

• 2 Brit. informal (especially among cockney men) an affectionate form of address for a girl or woman.

– origin ME: via OFr. from med. L. ducissa, from L. dux, duc- (see duke).