Not so (4)
'not so' is the definition.
(eg 'not so big' means 'less big')
This is the entire clue.
(Other definitions for less that I've seen before include "Minus; not so much" , "In smaller quantity" , "See 12" , "more, as they say" , "minor" .)
(Other definitions for lies that I've seen before include "Fabrications" , "Reclines" , "Wallows" , "Deceits; is" , "pork pies" .)
(Other definitions for liar that I've seen before include "One telling untruths" , "man of fiction?" , "Untruthful person (Billy in Schlesinger film)" , "Teller of fibs" , "Dissembler" .)
'not so' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for false that I've seen before include "Invalid; untrue" , "Unfaithful" , "Erroneous" , "Untrue - treacherous - counterfeit" , "Bogus" .)