Old Bill very precise (5)

I believe the answer is:

exact

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'precise' is the definition.
(associated in meaning)

'old bill very' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'bill very' becomes 'act' (I've seen this in other clues. I am not sure about the 'very' bit.).
'ex'+'act'='EXACT'

Can you help me to learn more?

(Other definitions for exact that I've seen before include "accurate in all details" , "without rounding" , "Strict" , "Precisely accurate" , "on the money" .)

I've seen this clue in The Sun.

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