One aim — blocking hunt that’s cruel (8)

I believe the answer is:

fiendish

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'cruel' is the definition.
(I've seen this in another clue)

'one aim blocking hunt' is the wordplay.
'one' becomes 'i' (Roman numeral).
'aim' becomes 'end' (both can mean a goal or purpose).
'blocking' is an insertion indicator (block can mean to plug a gap in something).
'hunt' becomes 'fish' (I am not sure about this - if you are sure you should believe this answer much more).
'i'+'end'='iend'
'iend' placed into 'fish' is 'FIENDISH'.

'that's' acts as a link.

Can you help me to learn more?

(Other definitions for fiendish that I've seen before include "Very difficult" , "This Sudoku" , "like some Sudokus" , "Infernal" , "Terrible" .)

I've seen this clue in The Sunday Times.

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