Something to make fast (5)

I believe the answer is:

haste

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'fast' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I don't see?

I don't understand the rest of the clue.

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(Other definitions for haste that I've seen before include "More of this can slow you up!" , "Speed, hurry" , "Expedition" , "go at speed" , "Possible cause of careless mistakes?" .)

I've seen this clue in the Evening Standard.

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