Arduous (adjective)

1. Requiring great effort or exertion; hard to do or accomplish.
2. Mentally or physically demanding and tiring.

Origin:

Late 16th century: from latin arduus "steep, high", from ardere "burn, be on fire".

Examples:

1. Climbing Mount Everest is an arduous task that requires months of preparation and training.
2. The journey through the desert was long and arduous.
3. The examination was an arduous test of their knowledge and skill.
4. The task was arduous, but he was determined to see it through.
5. The arduous work of building the bridge took several years to complete.