Obligation (noun)
احسان، فرض
an act or course of action to which a person is morally or legally bound; a duty or commitment.
Example: “I have an obligation to look after her”
Onerous (adjective)
سخت ، کڑا، مشکل، بھاری
(of a task or responsibility) involving a great deal of effort, trouble, or difficulty.
Example: “he found his duties increasingly onerous”