DICT.TW Dictionary Taiwan

 de ri·gueur /də(ˌ)riˈgɚ/

 De ri·gueur  According to strictness (of etiquette, rule, or the like); obligatory; strictly required.
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 de rigueur
      adj : required by etiquette or usage or fashion; "instruction as
            to when and where a silk hat is de rigueur"