not easily borne; wearing; "the burdensome task of preparing the income tax return"; "my duties weren't onerous; I only had to greet the guests"; "a taxing schedule"
If you describe a task as onerous, you dislike having to do it because you find it difficult or unpleasant. parents who have had the onerous task of bringing up a very difficult child. work or a responsibility that is onerous is difficult and worrying or makes you tired (onereus, from onerosus, from onus; ONUS)