1) Called for 2) French word used in English 3) Proper 
• According to strictness (of etiquette, rule, or the like); obligatory; strictly required.
De ri`gueur' [ French See 2d Rigor .] According to strictness (of etiquette, rule, or the like); obligatory; strictly required. 
[adj] - required by etiquette or usage or fashion
adjective required by etiquette or usage or fashion; `instruction as to when and where a silk hat is de rigueur`
strictly required, as by etiquette, usage, or fashion.