[oner.ous] adj [ME, fr. MF onereus, fr. L onerosus, fr. oner-, onus burden; akin to Skt anas cart] (14c) 1: involving, imposing, or constituting a burden: troublesome "an ~ task"
2: having legal obligations that outweigh the advantages "~ contract" -- oner.ous.ly adv -- oner.ous.ness n syn onerous, burdensome, oppressive, exacting mean imposing hardship. onerous stresses being laborious and heavy esp. because distasteful "the onerous task of cleaning up the mess". burdensome suggests causing mental as well as physical strain "burdensome responsibilities". oppressive implies extreme harshness or severity in what is imposed "the oppressive tyranny of a police state". exacting implies rigor or sternness rather than tyranny or injustice in the demands made or in the one demanding "an exacting employer".