DECORUM Meaning of DECORUM in English [ dɪ'kɔ:rəm ]■ noun behaviour in keeping with good taste and propriety. ↘customary behaviour; etiquette.OriginC16: from L., neut. of the adjective decorus 'seemly'. Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004