Laborious means requiring a lot of hard work, effort, and time. When a task is laborious, it takes sustained effort and patience to complete. Writing an essay by hand might be laborious if you have to carefully copy each word. Digging a garden bed with a shovel is laborious work compared to using a machine.

It emphasizes that something demands prolonged physical or mental effort. Building a stone wall is laborious because you must move and place each heavy stone carefully. Reading through a badly organized textbook to find information can be laborious because it requires so much time and concentration.

Notice that laborious doesn't mean impossible or even especially hard intellectually. It means requiring steady, sustained work. Copying an entire book word for word wouldn't be complicated, but it would certainly be laborious. Many important accomplishments in history came from laborious effort: the Great Wall of China, hand-illuminated medieval manuscripts, and the first detailed maps of the world.