FORMIDABLE

formidable, redoubtable, unnerving

(adjective) inspiring fear; “the formidable prospect of major surgery”; “a tougher and more redoubtable adversary than the heel-clicking, jackbooted fanatic”- G.H.Johnston; “something unnerving and prisonlike about high grey wall”

formidable

(adjective) extremely impressive in strength or excellence; “a formidable opponent”; “the challenge was formidable”; “had a formidable array of compositions to his credit”; “the formidable army of brains at the Prime Minister’s disposal”

Source: WordNet® 3.1

Etymology

Adjective

formidable (comparative more formidable, superlative most formidable)

Causing fear, dread, awe, or discouragement as a result of size, strength, or some other impressive feature; commanding respect; causing wonder or astonishment.

Difficult to defeat or overcome.

Source: Wiktionary

For"mi*da*ble, a. Etym: [L. formidabilis, fr. formidare to fear, dread: cf. F. formidable.]

Definition: 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.

Syn.

– Dreadful; fearful; terrible; frightful; shocking; horrible; terrific; tremendous.

Source: Webster’s Unabridged Dictionary 1913 Edition