Onerous

adjective/on-er-us/

Meaning

(of a task, duty, or responsibility) involving an amount of effort and difficulty that is oppressively burdensome.

In context
The onerous task took much longer than expected.

Remember it

Onus means burden — an onerous job loads a heavy onus onto your shoulders.

Use it well

For duties and tasks, not people: onerous chores, an onerous responsibility.