Herculean, abstruse, allergic, anaphylactic, arduous, awkward, brutal, capricious, changeable, complex, critical, dangerous, delicate, demanding, desultory, difficile, difficult, empathetic, empathic, exacting, fickle, formidable, fragile, goosy, hairy, hard-earned, hard-fought, hard, hazardous, high-strung, hyperesthetic, hyperpathic, hypersensitive, infirm, insecure, insubstantial, intricate, irritable, itchy, jawbreaking, knotted, knotty, laborious, mean, mercurial, miffy, nervous, no picnic, not easy, on slippery ground, on thin ice, operose, overrefined, oversensible, oversensitive, overtender, passible, perilous, precarious, prickly, provisional, refined, responsive, rigorous, risky, rocky, rough, rugged, sensitive, set with thorns, severe, shaky, shifting, shifty, skittish, slippery, slippy, spiny, steep, strenuous, supersensitive, sympathetic, tactful, temperamental, temporary, tender, tentative, tetchy, thin-skinned, thorny, tickling, tickly, titillative, toilsome, touch-and-go, touchy, tough, treacherous, tricky, uncertain, undependable, unfaithworthy, unreliable, unsettled, unsolid, unsound, unstable, unsteadfast, unsteady, unsubstantial, unsure, untrustworthy, uphill, variable, volatile, wicked