Definition of difficult :
1. Hard to do or to make; beset with difficulty; attended with labor, trouble, or pains; not easy; arduous.
2. Hard to manage or to please; not easily wrought upon; austere; stubborn; as, a difficult person.
3. To render difficult; to impede; to perplex.
vexed, catchy, embarrassing, contrarious, challenging, pathless, strong, intemperate, rambling, hard-fought, wayward, fractious, digressive, serious, simple, unintelligible, delicate, unknown, nasty, gruelling, enigmatic, unenviable, ambitious, punishing, manageable, support, hidden, froward, mystical, comfort, tall, titanic, exacting, weighty, tangled, careful, esoteric, subtle, backbreaking, labored, clear, vexatious, incommodious, unwieldy, unfathomable, grueling, impossible, sticky, inexplicable, exigent, unmanageable, equivocal, deep, immense, inscrutable, labyrinthine, Gargantuan, awkward, confusing, problematical, uncorrectable, rigorous, tedious, uncontrollable, steep, irksome, voiceless, operose, stiff, unclear, unaccountable, easy, balky, profound, irritable, inconvenient, perverse, occult, inconceivable, rocky, effortful, recondite, unvoiced, unyielding, knockout, surd, hairy, metaphysical, problematic, turgid, exhausting, incomprehensible, meandering, ambiguous, baffling, ornery, trackless, stubborn, loose, mystifying, taxing, concealed, attitude, paradoxical, concentrated, abstract, herculean, painful, heavy, dark, obstinate
adverse (part of speech: adjective)
distressful, unlucky, burdensome, inauspicious, hard, unfortunate, disastrous, calamitous, unfavorable, adverse, tragic, miserable, perilous, antipathetic, woeful, unpropitious, troublesome, untoward, opposing, detrimental, catastrophic, unfriendly, grievous
difficult (part of speech: adjective)
harsh, severe, finicky, uphill, fussy, oppressive, cantankerous, stressful, demanding, wearying, arduous, onerous, contrary, cumbersome, wearing, toilsome, knotty, wearisome, rugged, ticklish, laborious, tight, rough, bothersome, grinding, formidable, tough, tricky, thorny, strenuous, trying
complex (part of speech: adjective)