1.  impropriety(n = noun.attribute) improperness - an improper demeanor;
is a kind of behavior, behaviour, conduct, demeanor, demeanour, deportment
has particulars: incorrectness, inappropriateness, wrongness, indelicacy, indecorousness, indecorum, indecency
Antonym: propriety

2.  impropriety(n = noun.state) - the condition of being improper;
is a kind of condition, status

3.  impropriety(n = noun.act) indecency - an indecent or improper act;
is a kind of misbehavior, misbehaviour, misdeed
has particulars: obscenity

4.  impropriety(n = noun.act) familiarity, indecorum, liberty - an act of undue intimacy;
is a kind of misbehavior, misbehaviour, misdeed

1.  The quality of being improper; unfitness or unsuitableness to character, time place, or circumstances; as, impropriety of behavior or manners. [1913 Webster]

2.  That which is improper; an unsuitable or improper act, or an inaccurate use of language. [1913 Webster]
"But every language has likewise its improprieties and absurdities." [1913 Webster]
"Many gross improprieties, however authorized by practice, ought to be discarded." [1913 Webster]

impropriety, n. (pl. -ies)
1 lack of propriety; indecency.
2 an instance of improper conduct etc.
3 incorrectness.
4 unfitness.

Etymology:
F impropri{eacute}t{eacute} or L improprietas (as IN-(1), proprius proper)

N  solecism, bad grammar, false grammar, faulty grammar, slip of the pen, slip of the tongue, lapsus linguae, slipslop, bull, barbarism, impropriety, ungrammatical, incorrect, inaccurate, faulty, improper, incongruous, solecistic, solecistical.

N  inexpedience, inexpediency, undesirableness, undesirability, discommodity, impropriety, unfitness, inutility, disadvantage, inexpedient, undesirable, unadvisable, inadvisable, objectionable, inapt, ineligible, inadmissible, inconvenient, incommodious, discommodious, disadvantageous, inappropriate, unfit, ill-contrived, ill-advised, unsatisfactory, unprofitable, unsubservient, inopportune, out of place, in the wrong place, improper, unseemly, clumsy, awkward, cumbrous, cumbersome, lumbering, unwieldy, hulky, unmanageable, impedient, unnecessary, it will never do.

N  disagreement, discord, discordance, dissonance, dissidence, discrepancy, unconformity, incongruity, incongruence, discongruity, mesalliance, jarring, dissension, conflict, bickering, clashing, misunderstanding, wrangle, disparity, mismatch, disproportion, dissimilitude, inequality, disproportionateness, variance, divergence, repugnance, unfitness, inaptitude, impropriety, inapplicability, inconsistency, inconcinnity, irrelevancy, misjoining, misjoinder, syncretism, intrusion, interference, concordia discors, fish out of water, disagreeing, discordant, discrepant, at variance, at war, hostile, antagonistic, repugnant, incompatible, irreconcilable, inconsistent with, unconformable, exceptional, intrusive, incongruous, disproportionate, disproportionated, inharmonious, unharmonious, inconsonant, unconsonant, divergent, repugnant to, inapt, unapt, inappropriate, improper, unsuited, unsuitable, inapplicable, not to the point, unfit, unfitting, unbefitting, unbecoming, illtimed, unseasonable, mal a propos, inadmissible, inapposite, uncongenial, ill-assorted, ill-sorted, mismatched, misjoined, misplaced, misclassified, unaccommodating, irreducible, incommensurable, uncommensurable, unsympathetic, out of character, out of keeping, out of proportion, out of joint, out of tune, out of place, out of season, out of its element, at odds with, at variance with, in defiance, in contempt, in spite of, discordantly, a tort et a travers, asinus ad lyram.

N  undueness, malum prohibitum, impropriety, illegality, falseness, emptiness of title, invalidity of title, illegitimacy, loss of right, disfranchisement, forfeiture, usurpation, tort, violation, breach, encroachment, presumption, assumption, seizure, stretch, exaction, imposition, lion's share, usurper, pretender, undue, unlawful, unconstitutional, illicit, unauthorized, unwarranted, disallowed, unallowed, unsanctioned, unjustified, unentitled, disentitled, unqualified, disqualified, unprivileged, unchartered, illegitimate, bastard, spurious, supposititious, false, usurped, tortious, undeserved, unmerited, unearned, unfulfilled, forfeited, disfranchised, improper, unmeet, unfit, unbefitting, unseemly, unbecoming, misbecoming, seemless, contra bonos mores, not the thing, out of the question, not to be thought of, preposterous, pretentious, would-be, filius nullius.

N  vice, evil-doing, evil courses, wrongdoing, wickedness, viciousness, iniquity, peccability, demerit, sin, Adam, old Adam, offending Adam, immorality, impropriety, indecorum, scandal, laxity, looseness of morals, enphagy, dophagy, exophagy, want of principle, want of ballast, obliquity, backsliding, infamy, demoralization, pravity, depravity, pollution, hardness of heart, brutality, corruption, knavery, profligacy, flagrancy, atrocity, cannibalism, lesbianism, Sadism, infirmity, weakness, weakness of the flesh, frailty, imperfection, error, weak side, foible, failing, failure, crying sin, besetting sin, defect, deficiency, cloven foot, lowest dregs of vice, sink of iniquity, Alsatian den, gusto picaresco, fault, crime, criminality, sinner, brothel, gambling house, joint, opium den, shooting gallery, crack house, vicious, sinful, sinning, wicked, iniquitous, immoral, unrighteous, wrong, criminal, naughty, incorrect, unduteous, undutiful, unprincipled, lawless, disorderly, contra bonos mores, indecorous, unseemly, improper, dissolute, profligate, scampish, unworthy, worthless, desertless, disgraceful, recreant, reprehensible, blameworthy, uncommendable, discreditable, disreputable, Sadistic, base, sinister, scurvy, foul, gross, vile, black, grave, facinorous, felonious, nefarious, shameful, scandalous, infamous, villainous, of a deep dye, heinous, flagrant, flagitious, atrocious, incarnate, accursed, Mephistophelian, satanic, diabolic, hellish, infernal, stygian, fiendlike, hell-born, demoniacal, devilish, fiendish, miscreated, misbegotten, demoralized, corrupt, depraved, evil-minded, evil-disposed, ill-conditioned, malevolent, heartless, graceless, shameless, virtueless, abandoned, lost to virtue, unconscionable, sunk in iniquity, lost in iniquity, steeped in iniquity, incorrigible, irreclaimable, obdurate, reprobate, past praying for, culpable, reprehensible, unjustifiable, indefensible, inexcusable, inexpiable, unpardonable, irremissible, weak, frail, lax, infirm, imperfect, indiscrete, demoralizing, degrading, wrong, sinfully, without excuse, Int, O tempora!, O mores!, alitur vitium vivitque tegendo, genus est mortis male vivere, mala mens malus animus, nemo repente fuit turpissimus, the trail of the serpent is over them all, to sanction vice and hunt decorum down.