Sentence:  The multi-millionaire [Alexander Thynn, 7th Marquess of Bath] named his numerous girlfriends <WSD>wifelets</WSD> when he embarked on his "polyamorous" lifestyle shortly after marrying in 1969. [...] The trouble between two of the women erupted on Sunday night as a fight broke out in his Wiltshire stately home, Longleat – famed for its safari park lions. As the <WSD>wifelets</WSD> fought for his affections Lord Bath retired to his bedroom, which is decorated with murals inspired by the Kama Sutra, the Indian sex manual. 
Meaning of the word marked with <WSD> tags:  A long-term girlfriend; a (t=the other woman in an extramarital relationship). (from 1960s)