arduous
UK: ˈɑːdʒuəs | US: ˈɑːrdʒuəs
adj. requiring great effort; difficult and tiring
adj. hard to accomplish; demanding considerable exertion
The word arduous traces back to Latin arduus, meaning "high, steep," which metaphorically evolved to signify "difficult" or "challenging." The suffix -ous (from Latin -osus) turns it into an adjective, emphasizing a quality of being "full of difficulty." The imagery of climbing a steep slope vividly captures the word's modern sense of strenuous effort.
The hike up the mountain was arduous but rewarding.
She completed the arduous task of translating the ancient manuscript.
Training for the marathon proved to be an arduous process.
The team faced an arduous journey through the desert.
Writing a thesis is often an arduous undertaking.