Get a move on; is holding X (6)

I believe the answer is:

hasten

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'get a move on' is the definition.
(I've seen this in another clue)

'holding x' is the wordplay.
'holding' becomes 'has' (I can't explain this - if you can you should give a lot more credence to this answer).
'x' becomes 'ten' (X is the Roman numeral for ten).
'has'+'ten'='HASTEN'

'is' is the link.

Can you help me to learn more?

(Other definitions for hasten that I've seen before include "Hurry up in old-fashioned way" , "Travel with expedition" , "dash" , "Hurry along" , "Make faster" .)

I've seen this clue in the Sydney Morning Herald.

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