adj. 25B6; adjective
a formidable curved dagger : INTIMIDATING, forbidding, daunting, disturbing, alarming, frightening, disquieting, brooding, awesome, fearsome, ominous, foreboding, sinister, menacing, threatening, dangerous.
a formidable task : ONEROUS, arduous, taxing, difficult, hard, heavy, laborious, burdensome, strenuous, back-breaking, uphill, Herculean, monumental, colossal; demanding, tough, challenging, exacting; formal exigent; archaic toilsome.
a formidable pianist : CAPABLE, able, proficient, adept, adroit, accomplished, seasoned, skilful, skilled, gifted, talented, masterly, virtuoso, expert, knowledgeable, qualified; impressive, powerful, mighty, terrific, tremendous, great, complete, redoubtable; informal mean, wicked, deadly, nifty, crack, ace, wizard, magic; N. Amer. informal crackerjack.
pleasant-looking, comforting, easy, poor, weak.