grueling

[ groo-uh-ling, groo-ling ]

/ ˈgru ə lɪŋ, ˈgru lɪŋ /

exhausting; very tiring; arduously severe: the grueling Boston marathon.

any trying or exhausting procedure or experience.

Also especially British, gru·el·ling.

Origin of grueling

1850–55; slang gruel punishment (noun), punish (v.) + -ing², -ing¹

gru·el·ing·ly, adverb

grudge, grudging, grudziadz, grue, gruel, grueling, gruelling, gruenberg, gruesome, gruff, gruffy

Some might lack the fortitude—or masochism—required to endure a grueling campaign (Rubio).

What Republicans Need Right Now Is a Good Internal Fight |James Poulos |November 6, 2014 |DAILY BEAST
In a grueling two-hour questioning, Carter provided testimony as to why the drug can be useful in pain management.

Judge Could Smash Marijuana Law |Abby Haglage |November 4, 2014 |DAILY BEAST
Jaguar scored epic wins at the grueling Le Mans 24-hour race.

Nationalism on Four Wheels |Clive Irving |October 18, 2014 |DAILY BEAST
In June 1909, Model Ts were two of the first three finishers in a grueling New York-to-Seattle rally.

From the Model T to the Model S |The Daily Beast |September 24, 2014 |DAILY BEAST

After 15 hours of grueling interrogations, he was brought before judges and placed under formal investigation.

France’s Ex-Prez Sarkozy Placed Under Formal Investigation for Corruption |Tracy McNicoll |July 2, 2014 |DAILY BEAST
Arriving at the end of that grueling journey, he would rest for two days before making the return trip.

When the West Was Young |Frederick R. Bechdolt
It isn't a grueling competition like the 'Open' or even the 'Limit.'

Lad: A Dog |Albert Payson Terhune
He had been forced to stand out on the floor for twenty cruel, grueling minutes, to be a Horrible Example to a tittering class.

The Purple Heights |Marie Conway Oemler
If he was rested that day, on the morrow he would be fit for the grueling work possibly in store for him.

The Boy Scouts Book of Campfire Stories |Various
After a grueling examination, he admitted that he had crossed the line to smuggle in some tobacco.

The Secret Wireless |Lewis E. Theiss