n. [ Pref. in- not + decorum: cf. L. indecorous unbecoming. ] [ 1913 Webster ]

1. Lack of decorum; impropriety of behavior; that in behavior or manners which violates the established rules of civility, custom, or etiquette; indecorousness. [ 1913 Webster ]

2. An indecorous or unbecoming action. Young.

Syn. -- Indecorum 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. Indecency is the stronger word; indecorum refers to any transgression of etiquette or civility, especially in public. [ 1913 Webster ]