The French phrase de rigueur means “required,” “mandatory” (usually according to custom, etiquette, or fashion). It’s one of those tricky words like “liqueur” with a U before the E and another one after it. It is misspelled in a host of ways (de rigeur, de rigor, derigor, etc.) It is pronounced duh-ree-GUHR. Like other incompletely adopted foreign phrases, it is usually italicized in print.
BUY THE BOOK!