improper (adj.)
- aberrant
- abnormal
- abominable
- amiss
- arrant
- atrocious
- bad
- barbaric
- barbarous
- base
- black
- blamable
- blameworthy
- cacophonous
- careless
- chintzy
- clumsy
- coarse
- corrupt
- criminal
- crude
- damnable
- dark
- delinquent
- deviant
- disgraceful
- disorderly
- disruptive
- dysphemistic
- erroneous
- evil
- excessive
- execrable
- false
- faulty
- flagitious
- flagrant
- foul
- fresh
- futile
- gauche
- graceless
- gross
- harsh
- heinous
- ignominious
- ill
- ill-advised
- ill-chosen
- ill-considered
- ill-sorted
- ill-timed
- illegal
- immodest
- immoral
- impertinent
- impolite
- impolitic
- imprecise
- impure
- inaccurate
- inadmissible
- inadvisable
- inapplicable
- inapposite
- inappropriate
- inapt
- inauspicious
- incompatible
- incongruous
- inconvenient
- incorrect
- indecent
- indecorous
- indelicate
- indiscreet
- inelegant
- inept
- inexact
- inexpedient
- infamous
- infelicitous
- inferior
- informal
- iniquitous
- inopportune
- intrusive
- invalid
- irregular
- irrelevant
- knavish
- lascivious
- late
- lewd
- loose
- low
- maladjusted
- malapropos
- malevolent
- malodorous
- mismatched
- mismated
- misplaced
- mistaken
- monstrous
- naughty
- nefarious
- obscene
- off-base
- off-color
- offensive
- outlandish
- peccant
- premature
- rank
- reprehensible
- reprobate
- risque
- rough
- rowdy
- rude
- ruffianly
- sacrilegious
- sassy
- scandalous
- shameful
- shameless
- sinful
- sinister
- slipshod
- slovenly
- suggestive
- tactless
- tasteless
- terrible
- unadapted
- unbecoming
- unbefitting
- uncalled-for
- unceremonious
- uncomely
- unconventional
- uncouth
- undesirable
- undignified
- undue
- unfavorable
- unfit
- unfitting
- unforgivable
- unfortunate
- ungodly
- ungraceful
- unhappy
- unhealthy
- unkind
- unlawful
- unlucky
- unpardonable
- unpleasant
- unpolished
- unprofitable
- unpropitious
- unqualified
- unready
- unrefined
- unrighteous
- unripe
- unseasonable
- unseemly
- unskillful
- unspeakable
- unsuitable
- unsuited
- untimely
- untoward
- untrue
- unwise
- unworthy
- vicious
- vile
- villainous
- vulgar
- wicked
- wrong
- wrongful
