“difficult”

Requiring great effort or endurance to accomplish.

“The arduous climb to the summit left even the seasoned hikers breathless.”

Best for: Works well in formal writing or when describing physical or emotional struggle.

Inspiring fear or respect through being impressively demanding.

“She faced a formidable stack of legal briefs before the morning hearing.”

Best for: Great for emphasizing scale or intimidation alongside difficulty.

Exhaustingly severe or demanding in a way that wears one down.

“The grueling marathon through desert heat claimed a third of the competitors.”

Best for: Punchy and visceral — ideal for journalism, sports, or action writing.

Involving a burdensome amount of effort, obligation, or trouble.

“The onerous paperwork required to adopt a child surprised even their lawyer.”

Best for: Best in legal, professional, or literary contexts to convey oppressive difficulty.

Abstruse and difficult to understand due to obscurity or complexity.

“The professor's recondite lectures left even doctoral students quietly bewildered.”

Best for: Reserved for intellectual or academic difficulty; signals deep obscurity.

Endlessly laborious and futile, like the mythological task of rolling a boulder uphill forever.

“Keeping the inbox at zero felt like a Sisyphean battle she could never win.”

Best for: Literary and allusive — powerful when difficulty feels endless or absurd.