Found 20 stronger alternatives to upgrade your writing.
Not easy (general)
Nuance: Challenging
Standard replacement.
Boring
It was a hard test.
Better
It was a difficult test.
Strong / difficult
Nuance: Strong
Strength or difficulty.
Boring
He is a hard guy.
Better
He is a tough guy.
Not soft (physical)
Nuance: Firm
Physical state.
Boring
The ground is hard.
Better
The ground is solid.
Lots of work
Nuance: Physical
Physical effort.
Boring
It was hard labor.
Better
It was heavy labor.
Tests ability
Nuance: Growth-focused
Positive difficulty (growth).
Boring
The puzzle was hard.
Better
The puzzle was challenging.
Complicated
Nuance: Complicated
Many parts.
Boring
The problem is hard.
Better
The problem is complex.
Requires effort
Nuance: Strict
Expects a lot.
Boring
The job is hard.
Better
The job is demanding.
Rigid (physical)
Nuance: Rigid
Rigidity.
Boring
The cardboard is hard.
Better
The cardboard is stiff.
Solid / strict
Nuance: Supportive
Supportive/solid.
Boring
The mattress is hard.
Better
The mattress is firm.
Cruel / severe
Nuance: Severe
Severity.
Boring
The punishment was hard.
Better
The punishment was harsh.
Physical effort
Nuance: Exhausting
Sweaty effort.
Boring
It was a hard hike.
Better
It was a strenuous hike.
Serious / extreme
Nuance: Extreme
Extreme conditions.
Boring
The winter was hard.
Better
The winter was severe.
Lots of work (time)
Nuance: Slow/Work
Slow effort.
Boring
Writing the book was hard.
Better
Writing the book was laborious.
Very difficult (effort)
Nuance: Painful
Painful effort.
Boring
The journey was hard.
Better
The journey was arduous.
Strict / thorough
Nuance: Strict
High standards.
Boring
The training is hard.
Better
The training is rigorous.
Scary / difficult
Nuance: Scary
Respect/fear.
Boring
A hard opponent.
Better
A formidable opponent.
Cannot get through
Nuance: Blocked
Physical barrier.
Boring
The wall was hard to get through.
Better
The wall was impenetrable to get through.
Unfeeling (emotional)
Nuance: Cruel
Lack of empathy.
Boring
He has a hard heart.
Better
He has a callous heart.
Detailed difficulty
Nuance: Detailed
Complexity of detail.
Boring
The design is hard.
Better
The design is intricate.
Exhausting
Nuance: Punishing
Punishing effort.
Boring
The race was hard.
Better
The race was grueling.