"decorous" in the adjective sense
characterized by propriety and dignity and good taste in manners and conduct
"the tete-a-tete was decorous in the extreme"
2. becoming, comely, comme il faut, decorous, seemly
according with custom or propriety
"her becoming modesty"
"it is not comme il faut for a gentleman to be constantly asking for money"
Source: WordNet® (An amazing lexical database of English)
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