False, incorrect (6)
I believe the answer is:
untrue
This clue is a double definition.
'false' is the first definition.
(similar in meaning)
'incorrect' is the second definition.
(I've seen this in another clue)
(Other definitions for untrue that I've seen before include "Not faithful" , "Incorrect or false" , "Wrong" , "like the magnetic north?" , "Legendary" .)