Wasted pound found in street (5)
I believe the answer is:
spent
'wasted' is the definition.
(thesaurus)
'pound found in street' is the wordplay.
'pound' becomes 'pen' (both can mean an animal enclosure).
'found in' means one lot of letters goes inside another.
'street' becomes 'st' (abbreviation).
'pen' put inside 'st' is 'SPENT'.
(Other definitions for spent that I've seen before include "Paid out - finished" , "Burned-out" , "Used up; exhausted" , "Worn out - after shopping?" , "Worn out, having laid out money" .)