causing fear, apprehension, or dread

a formidable opponent.

of discouraging or awesome strength, size, difficulty, etc.; intimidating

a formidable problem.

arousing feelings of awe or admiration because of grandeur, strength, etc.

of great strength; forceful; powerful

formidable opposition to the proposal.

adjective

feeble , friendly , harmless , nice , pleasant , powerless , weak , easy , not hard , trivial

adjective

appalling , awful , dangerous , daunting , dire , dismaying , dreadful , fearful , fierce , frightful , horrific , imposing , impregnable , intimidating , menacing , redoubtable , shocking , terrible , terrific , threatening , all-powerful , arduous , awesome , ballbuster , challenging , colossal , effortful , great , hard , impressive , indomitable , labored , laborious , mammoth , mighty , murder * , onerous , overpowering , powerful , puissant , rough * , rough go , staggering , strenuous , tall order , toilsome , tough * , tough proposition , tremendous , uphill * , direful , fearsome , ghastly , scary , backbreaking , demanding , difficult , exacting , exigent , heavy , oppressive , rigorous , rough , severe , taxing , tough , trying , weighty , alarming , horrible