Onerous

difficult hard demanding heavy severe taxing strenuous laborious arduous tiring exhausting grueling fatiguing tiresome backbreaking toilsome burdensome oppressive crushing overpowering intolerable distressing painful grave serious responsible exacting rigorous formidable pressing exigent ponderous weighty excessive grinding harrowing merciless galling harsh irksome troublesome vexatious cumbersome austere headache embittering overtaxing plodding