It's spelled _Hors d'œuvre_ in French, using the weird ligature of o and e[1]. According to the Wikipedia article:
> A number of words written with œ were borrowed from French and from Latin into English, where the œ is now rarely written. Modern American English spelling usually substitutes e, so diarrhœa has become diarrhea, although there are some exceptions, such as _phoenix_. In modern British English, the spellings generally keep the o but remove the ligature (e.g. diarrhoea).
In the case of _Hors d'oeuvre_, it seems like the english wikipedia keeps the _o_. [2]
[1]: https://en.wikipedia.org/wiki/%C5%92
[2]: https://en.wikipedia.org/wiki/Hors_d%27oeuvre
