Counterfeit pound discovered in broken safe (5)
I believe the answer is:
false
'counterfeit' is the definition.
(associated in meaning)
'pound discovered in broken safe' is the wordplay.
'pound' becomes 'L' (the pound sign is based on an L).
'discovered in' means one lot of letters goes inside another.
'broken' indicates an anagram.
'safe' with letters rearranged gives 'fase'.
'l' placed within 'fase' is 'FALSE'.
(Other definitions for false that I've seen before include "Not true" , "Erroneous" , "Bogus" , "Untrue - treacherous - counterfeit" , "Not genuine or real" .)