Antagonistic, Arduous, Besetting, Bothersome, Burdensome, Conflicting, Contrary, Counter, Crushing, Demanding, Detrimental, Difficult, Dispiriting, Disquieting, Distressing, Draining, Empirical, Enervating, Exacting, Examining, Exasperating, Exhausting, Exigent, Experimental, Exploratory, Fatiguing, Feeling, Frustrating, Groping, Grueling, Hard, Harmful, Heavy, Hefty, Heuristic, Hostile, Infuriating, Inimical, Investigative, Investigatory, Irksome, Irritating, Killing, Maddening, Miserable, Onerous, Opposed, Opposing, Opposite, Oppressive, Painful, Pilot, Probationary, Probative, Proving, Provisional, Punishing, Rigorous, Rough, Sapping, Sinister, Sticky, Straining, Strenuous, Stressful, Taxing, Tentative, Test, Testing, Tiresome, Tiring, Tough, Trial, Tricky, Troublesome, Untoward, Upsetting, Vexatious, Adverse, Analytic, Annoying, Vexing, Weakening, Wearing, Wearisome, Wearying, Weighty, Worrisome, Worrying, Wretched