Crossword Genius

Choice of prudish sweetheart (5)

Ross

I believe the answer is:

prime

'choice' is the definition.
(I know that choice can be written as prime)

'prudish sweetheart' is the wordplay.
'prudish' becomes 'prim' (synonyms).
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'prim'+'e'='PRIME'

'of' is the link.

(Other definitions for prime that I've seen before include "Main - charge" , "Two or three, for example" , "Maybe eleven" , "Prepare for use, say a pump" , "(Of number) divisible only by itself and one" .)

I've seen this clue in The Telegraph.
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