tricky, formidable, insurmountable, challenging, difficult, arduous, complicated, doable, perilous, vexing, grueling, surmountable, toughest, prohibitive, dicey, problematic, herculean, scary, bewildering, grim, onerous, frightening, perplexing, unnerving, exhausting, fearsome, tempting, frustrating, unenviable, stressful, problematical, troublesome, monumental, tedious, unwieldy, impossible, nettlesome, weighty, thorny, conquerable, staggering, gargantuan, undaunted, laborious, ambitious, unsurmountable, sobering, dire, cumbersome, bleak, unfamiliar, straightforward, costly, confusing, mammoth, manageable, terrifying, easy, intriguing, unmanageable, tortuous, sisyphean, insuperable, enticing, disconcerting, faced, intractable, appetizing, unfathomable, undoable, unpalatable, impressive, precarious, unforgiving, humbling, improbable, exasperating, sterner, unappealing, stiff, attainable, unsettling, incongruous, unchartered, knottier, bumpy, unpromising, troubling, unfeasible, painful, dispiriting, alluring, unappetizing, maddening, accomplishable, treacherous, surprising, realistic, burdensome, ominous, torturous, plain sailing, abide, abrasive, absorbing, abstruse, accommodating, adept, admire, admiring, admits, ado, advan, advanced, agreeable, alarm, alarming, alert, alien, ancient, annoyance, boggling, awesome, baffling, taxing, disheartening, dismaying, demanding

discouraging, intimidating