Formidable

Part of speech: adjective (a.)

Exciting fear or apprehension; impressing dread; adapted to excite fear and deter from approach, encounter, or undertaking; alarming. They seemed to fear the formodable sight. Dryden. I swell my preface into a volume, and make it formidable, when you see so many pages behind. Drydn.

Synonyms: Dreadful; fearful; terrible; frightful; shocking; horrible; terrific; tremendous.