Not true (5)
'not true' is the definition.
('false' is the opposite to 'true')
This is the entire clue.
(Other definitions for false that I've seen before include "Incorrect" , "Spurious, untrue" , "Bogus" , "Untrue - treacherous - counterfeit" , "Wrong" .)
'not true?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Another definition for at an angle that I've seen is " Obliquely".)