Danger the art is fake (6)
I believe the answer is:
threat
'danger' is the definition.
(threat is a kind of danger)
'the art is fake' is the wordplay.
'is fake' is an anagram indicator.
'the'+'art'='theart'
'theart' anagrammed gives 'THREAT'.
(Other definitions for threat that I've seen before include "Impending danger" , "Intimidation or warning" , "Possibility of danger" , "Hatter (anag)" , "The rat became a menace" .)