De rigueur \duh ri-GUR\ , adjective;
1. Strictly required, as by etiquette, usage, or fashion
This word is obviously French: rigueur means "strictness," so de regueur means "of strictness" (literal) and conveys a meaning of "according to obligation of convention."
This word is kind of boring, so let me refer you to a website that is an excellent diversion from work: http://www.etiquettehell.com
*Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Monday, November 15