INDECO'RUM, noun [Latin in and decorum.] Impropriety of behavior; that in behavior or manners which violates the established rules of civility, or the duties of respect which age or station requires; an unbecoming action. It is sometimes synonymous with indecency; but indecency, more frequently than indecorum is applied to words or actions which refer to what nature and propriety require to be concealed or suppressed.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI