Adjective

(en-adj)

Dreadful; causing alarm and fear.

Formidable, powerful.

* 1883: (Robert Louis Stevenson), (Treasure Island)

and there was even a party of the younger men who pretended to admire him, calling him a "true sea-dog," and "real old salt," and such-like names, and saying there was the sort of man that made England terrible at sea.

Intense; extreme in degree or extent.

* {{quote-book, year=1963, author=(Margery Allingham), title=(The China Governess)

, chapter=18 citation , passage=‘Then the father has a great fight with his terrible conscience,’ said Munday with granite seriousness. ‘Should he make a row with the police […]? Or should he say nothing about it and condone brutality for fear of appearing in the newspapers?}}

Unpleasant; disagreeable.

* , chapter=12

, title= The Mirror and the Lamp , passage=To Edward […] he was terrible , nerve-inflaming, poisonously asphyxiating. He sat rocking himself in the late Mr. Churchill's swing chair, smoking and twaddling.}}

Very bad; lousy.

* {{quote-news, year=2012, date=April 26, author=Tasha Robinson, work=The Onion AV Club

, title= Film: Reviews: The Pirates! Band Of Misfits , passage=The openly ridiculous plot has The Pirate Captain (Hugh Grant) scheming to win the Pirate Of The Year competition, even though he’s a terrible pirate, far outclassed by rivals voiced by Jeremy Piven and Salma Hayek.}}

Adjective

(head)

Unskilled, lacking normally expected degree of ability.

Having an incompetent lawyer may be grounds for a retrial, but the lawyer in question probably doesn't know that.

Unable to make rational decisions, insane or otherwise cognitively impaired.

The charged was judged incompetent to stand trial, at least until his medication started working.