wifelet

The story

From wife + -let (diminutive suffix). Sense 3 (“long-term girlfriend; mistress”) is said to have been coined in the 1960s by Alexander Thynn, 7th Marquess of Bath (1932–2020) in reference to his numerous mistresses.

First known use, by meaning

• from 1960s A long-term girlfriend; a mistress (the “other woman” in an extramarital relationship).