Untruthful person (4)
I believe the answer is:
liar
'untruthful person' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for liar that I've seen before include "Storyteller" , "Phoney" , "Tale-teller" , "Worse than a thief" , "Untruthful person (Billy in Schlesinger film)" .)