Found 22 stronger alternatives to upgrade your writing.
Short time
Nuance: Brief
Duration.
Boring
Just a fast question.
Better
Just a quick question.
Movement
Nuance: Active
Action-oriented.
Boring
A fast recovery.
Better
A speedy recovery.
Hurried (negative)
Nuance: Careless
Careless speed.
Boring
It was a fast job.
Better
It was a rushed job.
High rate
Nuance: High rate
Rate of change.
Boring
Fast growth.
Better
Rapid growth.
Smooth speed
Nuance: Efficient
Graceful/efficient.
Boring
A fast response.
Better
A swift response.
Happening at once
Nuance: Surprising
Unexpected.
Boring
A fast stop.
Better
A sudden stop.
Too fast / careless
Nuance: Careless
Warning against speed.
Boring
A fast decision.
Better
A hasty decision.
Energetic speed
Nuance: Energetic
Healthy/active.
Boring
A fast walk.
Better
A brisk walk.
On time / immediate
Nuance: Punctual
Polite/business.
Boring
A fast reply.
Better
A prompt reply.
Immediate
Nuance: Immediate
No wait.
Boring
Fast success.
Better
Instant success.
Fast movement (body)
Nuance: Flexible
Flexible speed.
Boring
The athlete is fast.
Better
The athlete is agile.
Right now
Nuance: Urgent
Urgency.
Boring
We need fast action.
Better
We need immediate action.
Increasing speed
Nuance: Increasing
Getting faster.
Boring
Fast learning.
Better
Accelerated learning.
Designed for speed
Nuance: Direct
System/service.
Boring
The fast train.
Better
The express train.
Passing quickly
Nuance: Short-lived
Disappearing.
Boring
A fast glimpse.
Better
A fleeting glimpse.
Efficiently fast (formal)
Nuance: Efficient
Formal word for speed with efficiency.
Boring
The process was fast.
Better
The process was expeditious.
Dangerously fast
Nuance: Dangerous
Danger.
Boring
Driving at fast speed.
Better
Driving at breakneck speed.
Very fast (intense)
Nuance: Intense
Heat/intensity.
Boring
A fast pace.
Better
A blistering pace.
Hasty / unwise
Nuance: Unwise
Foolish speed.
Boring
A fast action.
Better
A precipitate action.
Science: very high speed (hyphenated)
Nuance: Technical; very fast
Technical/science term; use as a hyphenated adjective.
Boring
The fast train reached the station in minutes.
Better
The high-velocity train reached the station in minutes.
Faster than sound
Nuance: Extreme
Literal speed.
Boring
Fast jet.
Better
Supersonic jet.
Rising very fast (fame)
Nuance: Impressive
Star-like.
Boring
Fast rise to fame.
Better
Meteoric rise to fame.