Trust buster (4)
I believe the answer is:
liar
'trust buster' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for liar that I've seen before include "Person regularly 'economical with the truth'" , "not straight [one]" , "27 [DECEIVER]" , "Dishonest person" , "Rail at a prevaricator" .)