onerous

raskas, rasittava impose imposing or constitute constituting a physical, mental, or figurative load which can be borne only with effort.
1820, w:Washington Irving|Washington Irving, "The Legend of Sleepy Hollow":

That all this might not be too onerous on the purses of his rustic patrons, who are apt to consider the costs of schooling a grievous burden, and schoolmasters as mere drones, he had various ways of rendering himself both useful and agreeable.

Again, and more intensely than ever, she desired a fixed occupation,—no matter how onerous, how irksome.

It has become an onerous duty, a wearisome and distasteful task.