Delayed fourth sailor in rush? (8)

I believe the answer is:

retarded

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'delayed fourth' is the definition.
'retarded' can be an answer for 'delayed' (thesaurus). I'm not sure about the 'fourth' bit.

'sailor in rush?' is the wordplay.
'sailor' becomes 'tar' (slang term for a sailor).
'in' is an insertion indicator.
'rush?' becomes 'reded' (I can't explain this - if you can you should give a lot more credence to this answer).
'tar' inserted within 'reded' is 'RETARDED'.

Can you help me to learn more?

(Other definitions for retarded that I've seen before include "Caused delay to, slowed progress" , "Delayed, slowed down" , "Underdeveloped" .)

I've seen this clue in The Sun.

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