This is an irregular feature - both in frequency and oddness - dedicated to a word I came across that I have never previously used.
mésalliance n. mistaken marriage; marriage into a lower social class.
From the French words més-, ("bad") alliance, ("alliance," "marriage")
Here is a quotation from the George Eliot novel Daniel Deronda (1876):
"It shows the Arrowpoints' good sense, however, to have adopted the affair, after the fuss in the paper," said Sir Hugo. "And disowning your own child because of a mésalliance is something like disowning your one eye: everybody knows it's yours, and you have no other to make an appearance with."