arduous

a long, arduous, and exhausting war.

Her delicate constitution disincline her from such an arduous job.

Long hours of arduous hiking tired the scouts.

The refugees made an arduous journey through the mountains.

Negotiating a reduction in nuclear arms is a long and arduous undertaking. See also Synonyms at firm 1

Learning a new role is a long and arduous undertaking.Demanding, rigorous, and exacting imply the imposition of severe and uncompromising demands:

The Shrinking of ChinaFor decades, rail travel in China meant an arduous overnighter in a crowded East German–designed train, riding along a rickety old track.