This adverbial use implies that something should happen without delay. For example, a fast response is expected in a fast-paced environment.
Please respond fast to my email.
I need a fast answer.
This meaning is related to choosing not to eat or drink for a period. People often fast for religious reasons or health benefits.
Many people fast for health reasons.
He decided to fast during Ramadan.
This meaning describes something that is fixed in place and cannot easily be moved. For example, an anchor is fast when holding a boat in position.
The anchor was fast in the water.
Make sure the load is fast before moving.
This meaning relates to quickly achieving a goal or turning events into action. For instance, fast-tracking a project means speeding up its progress.
She fasted through the night.
The project needs to fast-track approval.
