Speedy dash to make secure (6)

I believe the answer is:

fasten

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'make secure' is the definition.
(I've seen this before)

'speedy dash' is the wordplay.
'speedy' becomes 'fast' (similar in meaning).
'dash' becomes 'en' (I can't justify this - if you can you should give a lot more credence to this answer).
'fast'+'en'='FASTEN'

'to' acts as a link.

Can you help me to learn more?

(Other definitions for fasten that I've seen before include "Tie, secure" , "Fix -- make tight" , "Fix securely" , "Fix to, secure" , "Tie or join together, fix firmly" .)

I've seen this clue in The Sun.

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