The phrase "an onerous duty" is correct and usable in written English.
It can be used to describe a task or responsibility that is burdensome or difficult to bear.
Example: "As the team leader, I felt it was my onerous duty to ensure that every member was supported during the project."
Alternatives: "a heavy responsibility" or "a burdensome obligation."
J.S.P., posted on nytimes.com My wife and I discussed this article, and we determined that sex should be an onerous duty, undertaken only a few times, for the express purpose of creating the next generation.
Choreographers working in German municipal theaters are expected to provide "dance" wherever it is required -- operas, plays, operettas; many consider it an onerous duty, the price for having an ensemble and a budget.
The next year of his life found Albert once again appointed to an onerous duty.
An occupier has a less onerous duty towards a person "in the exercise of his calling", such as a professional or somebody exercising a trade.
But under the new plans the ministry has dropped a requirement for top bankers to prove they were unaware or had taken action to prevent misconduct at their institutions — known as "reverse burden of proof" — and instead introduce a less onerous "duty of responsibility" on such employees.
Why not give Handel's "Messiah" a break from its onerous duty as the requisite piece for the Christmas season and let "L'Enfance du Christ" take over for a while?
After performing this onerous duty (to a completely empty room), the gavel comes down again, and the session is closed.
Unlike traditional teaching environments where a variety of clinical teachers contribute to teaching in any given subject, in this program a single general / family practitioner was given the onerous duty of providing the vast majority of the teaching.
In many hospitals and clinics, medical scribes help spare the physician the onerous duty of documentation, thereby freeing up valued time to enable reconnection.
Fatou, the west African servant of the Derawal family in upscale Brondesbury Park, concludes that "she did not think she was a slave" despite the withheld passport and elusive wages; the onerous duties and the casual insults.
Officials have repeatedly talked of slapping a luxury tax on the purchase of new jets, on top of existing onerous duties and taxes.
