Unknown coin got in change (9)
I believe the answer is:
incognito
'unknown' is the definition.
(I've seen this before)
'coin got in change' is the wordplay.
'change' indicates an anagram.
'coin'+'got'+'in'='coingotin'
'coingotin' anagrammed gives 'INCOGNITO'.
(Other definitions for incognito that I've seen before include "as something else" , "In disguise" , "under another name" , "Without revealing one's identity" , "Anonymously" .)