This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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adj. Causing disgust or shock; horrifying.

adj. Causing fright; terrifying.

adj. Informal Excessive; extreme: a frightful liar.

adj. Informal Disagreeable; distressing: frightful weather.

adj. : Full of fright; affrighted; frightened.

adj. Full of that which causes fright; exciting alarm; impressing terror; shocking; as, a frightful chasm, or tempest; a frightful appearance.

adj. Used as an intensifier

adj. Full of fright; affrighted; frightened.

adj. Full of that which causes fright; exciting alarm; impressing terror; shocking.

Full of occasion for fright; causing or apt to excite alarm or terror; terrible; dreadful: as, a frightful chasm; a frightful tempest.

Intolerable; shocking; hideous.

Full of terror; fearful; alarmed.

Synonyms Dreadful, Fearful, etc. (see awful); alarming, terrific, horrible, shocking.

adj. extreme in degree or extent or amount or impact

adj. provoking horror

adj. extremely distressing

"His eyes were bright and glassy, and their expression frightful to look upon."

extraordinary    alarming    bad   

alarming    horrid    shocking    terrible    terrific    fearful    horrible    awful    dreadful    affrighted   

delightful    rightful    spiteful   

dreadful    horrid    appal    terrific    ghastly    monstrous    intolerable    dire    fatal