How to move a stop (4)

I believe the answer is:

whoa

'stop' is the definition.
(command to stop a horse)

'how to move a' is the wordplay.
'to move' indicates an anagram.
'how' anagrammed gives 'who'.
'who'+'a'='WHOA'

(Other definitions for whoa that I've seen before include "Danger" , "Hold your horses!" , "Stop! - steady on!" , "Command to horse to stop or stand still" , "Stop, Dobbin!" .)

I've seen this clue in The Guardian.

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