Fast

adj.energetic, capableeveryday

Meaning 1

Covering distance or completing an action in little time.

Reach for it when describing speed in movement, response, or work

A fast handover returned the emergency room to full capacity before noon.

playful
speedy
friendly, informal praise for prompt service is wanted
not when Avoid it in a technical report that needs a measured rate.
everyday
quick
a task or response takes little time
not when Quick suits a single action better than sustained high speed.
professional
efficient
little time or effort is wasted
not when Efficiency can be deliberate and slow; it is not proof of raw speed.
professional
prompt
the response begins without delay
not when Prompt does not say that the work itself was completed rapidly.
professional
rapid
measurable change or movement happens at a high rate
not when It can sound clinical when praising a lively person.
formal
swift
speed combines with decisiveness or grace
not when Swift is more polished than natural in casual conversation.

Firmly fixed so that movement or release is prevented.

Reach for it when using the less common sense found in fixed expressions

The climber checked that the rope remained fast to the anchor.

professional
secure
the attachment is safely held in place
not when Secure emphasizes safety, not the older idea of being tightly fixed.
literary
anchored
something is attached to a stable base
not when Anchored is too specific when no anchor or figurative foundation exists.

The definition and the example on this page are written here. The dictionaries above ground which meaning is being described, not the wording.