Took a possibly lost key (5)
I believe the answer is:
stole
'took' is the definition.
(stealing is a kind of taking)
'a possibly lost key' is the wordplay.
'a possibly' is an anagram indicator.
'key' becomes 'e' (I've seen this in other clues).
'lost' is an anagram of 'stol'.
'stol'+'e'='STOLE'
(Other definitions for stole that I've seen before include "Purloined; shawl" , "Long shawl" , "Pinched; wrap" , "Took unlawfully; shawl" , "Lifted" .)