Small quiet hack rushed (4)

I believe the answer is:

sped

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'rushed' is the definition.
('speed' can be a synonym of 'rush')

'small quiet hack' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'quiet hack' becomes 'ped' (I can't explain this - if you can you should give a lot more credence to this answer).
's'+'ped'='SPED'

Can you help me to learn more?

(Other definitions for sped that I've seen before include "Moved fast" , "Travelled quickly" , "Went quickly" , "Moved quickly" , "Went fast" .)

I've seen this clue in The Mirror.

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