Lyric discussion by EmilyPlay 

according to the oed, a "mésalliance" is anglicized french for 'a union between two people that is thought to be unsuitable or inappropriate; esp. a marriage with a person of a lower social position.'

I think that works, and it seems to be current given that the last citation was 1972.

shrug Dem Decemberists and dere obscure words!

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