jolie laide (n.)
"girl or woman whose attractiveness defies standards of beauty," 1849, a French expression (by 1780 in French), from fem. singular of joli "pretty" (see jolly) + laid "ugly," from Frankish *laid (see loath (adj.)).
Of beauty, as we narrowly understand it in England, [the 18c. French woman of society] had but little; but she possessed so many other witcheries that her habitual want of features and complexion ceased to count against her. Expression redeemed the absence of prettiness and the designation jolie laide was invented for her in order to express her power of pleasing despite her ugliness. ["The Decadence of French Women," Blackwood's Edinburgh Magazine, October 1881]