Could be roaming with us, but one doesn’t know (9)
I believe the answer is:
ignoramus
'one doesn't know' is the definition.
I can't tell whether this defines the answer.
'could be roaming with us' is the wordplay.
'could be' indicates anagramming the letters.
'with' is a charade indicator (letters next to each other).
'roaming' is an anagram of 'ignoram'.
'ignoram'+'us'='IGNORAMUS'
'but' is the link.
Can you help me to learn more?
(Other definitions for ignoramus that I've seen before include "I wouldn't know" , "Simpleton" , "One lacking knowledge" , "A know-nothing" , "One is not intelligent" .)