adjective

inspiring fear or respect through being impressively large, powerful, intense, or capable.

a formidable opponent

intimidating,forbidding,redoubtable,daunting,alarming,frightening,terrifying,petrifying,horrifying,chilling,disturbing,disquieting,dreadful,brooding,awesome,fearsome,ominous,foreboding,sinister,menacing,mean-looking,threatening,dangerous,spooky,scary,creepy,direful,bodeful,onerous,arduous,taxing,difficult,hard,heavy,laborious,burdensome,strenuous,vigorous,back-breaking,stiff,uphill,relentless,Herculean,monumental,colossal,demanding,trying,tough,challenging,exacting,overwhelming,exhausting,wearying,fatiguing,tiring,punishing,gruelling,grinding,killing,no picnic,knackering,toilsome,exigent,capable,able,proficient,adept,adroit,accomplished,impressive,strong,powerful,mighty,terrific,tremendous,great,indomitable,invincible,seasoned,skilful,skilled,gifted,talented,masterly,virtuoso,expert,knowledgeable,qualified,trained,efficient,good,excellent,brilliant,outstanding,first-class,first-rate,mean,wicked,deadly,nifty,crack,ace,stellar,wizard,magic,crackerjack,badass,compleat,habile,shit-hot