Use 'laborious' for tasks that take a lot of effort over an extended period. Completing the project was a laborious endeavor, extending late into the nights.
Pro Tip 2/3
Negative Nuance
'Laborious' often implies the work is not only hard but also somewhat dull or tedious. The laborious data entry work left the employees feeling exhausted and bored.
Pro Tip 3/3
Emphasis on Difficulty
The word 'laborious' highlights the difficulty rather than the importance of the activity. Though laborious, the job of sorting the files was necessary.