Synonyms for Unbecoming:

adj.

improper (adjective)
unbefitting, Unapt.
improper, unsuitable (adjective)
unseemly, indecent, unfit, awkward, uncomely, incongruous, salacious, malapropos, inappropriate, indecorous, unattractive, tasteless, tacky, indelicate, unbefitting, clumsy, inept, rough, unsightly, unworthy, unsuited, untoward, untimely, offensive, inapt.
inappropriate (adjective)
unsuited, inappropriate, unfit, malapropos, unsuitable, unbefitting, improper, ill-matched, of place, inapt, inapposite, out.
low (adjective)
undignified.
vulgar (adjective)
crass, unseemly, barnyard, homespun, cockney, depraved, chintzy, obscene, raw, common, earthy, tactless, outlandish, ill-bred, cheap, gaudy, brazen, ignoble, gross, tasteless, revolting, ignominious, tawdry, sleazy, colloquial, shameless, coarse-grained, coarse, vulgar, sordid, rough, rude, brutish, offensive, salty, indelicate, repulsive, graceless, profane, degraded, unpolished, low, inelegant, glaring, scandalous, idiomatic, in bad taste, broad, crude, base, unrefined, garish, undignified, barbaric, clumsy, philistine, animal, boorish, rank.

n.

inopportune, inconvenient, untimely. usual, unsightly, agree, ugly, plain, grotesque, inept, incongruous, unattractive, hideous, monstrous, Unapt, grim, unappealing. style, tacky. immodest, naughty. indecent (noun)
salacious, lewd, unworthy.
unbecoming (noun)
improper, untoward, unseemly, indecent, indecorous, uncomely, unwearable.
unsuitable (noun)
awkward.

Other synonyms:

inconvenient, inopportune. inept, immodest, untimely. naughty. incongruous, Unapt. undeserving
unworthy.
Other relevant words:
indecent, Unapt, inept, monstrous, awkward, untoward, naughty, ugly, grotesque, indecorous, grim, lewd, plain, inopportune, incongruous, tacky, untimely, unworthy, hideous, agree, unsightly, unattractive, uncomely, usual, unwearable, style, immodest, inconvenient, unappealing, salacious.

Usage examples for unbecoming

  1. It had been represented to the King that he ought not to be ready to regard financial concessions as a compliance unbecoming to the crown, for that in these matters he was at no disadvantage as compared with any person or any foreign power; that on the contrary the decision always proceeded from himself; that he was the head who cared for the welfare of the members. – A History of England Principally in the Seventeenth Century, Volume I (of 6) by Leopold von Ranke
  2. So far as I could learn no official action was taken by the Big Four because of conduct and language unbecoming a gentleman and a golfer. – Fore! by Charles Emmett Van Loan
  3. We all went down to the boat- house at eight o'clock, we girls with long coats over our light dresses, because it's silly to catch cold, and so unbecoming and on the way I told Will about Rachel. – The Heart of Una Sackville by Mrs. George de Horne Vaizey