Silly passport, possibly with nothing in it (5)
I believe the answer is:
idiot
'silly' is the definition.
(thesaurus)
'passport possibly with nothing in it' is the wordplay.
'passport possibly' becomes 'ID' (a passport is identification).
'with' is a charade indicator (letters next to each other).
'nothing' becomes 'O' (looks like zero - 0).
'in' indicates putting letters inside.
'o' put into 'it' is 'iot'.
'id'+'iot'='IDIOT'
(Other definitions for idiot that I've seen before include "Dolt" , "Oaf" , "Ass, nincompoop" , "The - (Dostoievsky)" , "Unwise person" .)