The word for today is…
arduous (adj) – 1. Demanding great effort or labour; difficult.
2. Testing severely the powers of endurance; strenuous.
3. Hard to traverse, climb, or surmount.
Source : The Free Dictionary
Etymology : “To forgive is the most arduous pitch human nature can arrive at.” When Richard Steele published that line in The Guardian in 1713, he was using arduous in what was apparently a fairly new way for English writers in his day: to imply that something was steep or lofty as well as difficult or strenuous. Steele’s use is one of the earliest documented in English for that meaning, but he didn’t commit it to paper until almost 150 years after the first uses of the word in its “strenuous” sense. Although the “steep” sense is newer, it is still true to the word’s origins; arduous derives from the Latin arduus, which means “high,” “steep,” or “difficult.”