Liar forced to complain (4)
I believe the answer is:
rail
'complain' is the definition.
(railing is a kind of complaining)
'liar forced' is the wordplay.
'forced' indicates an anagram.
'liar' anagrammed gives 'RAIL'.
'to' acts as a link.
(Other definitions for rail that I've seen before include "Bar; waterside bird" , "Protest strongly (at)" , "A bird; bar to hang on" , "Bar; waterbird" , "Horizontal bar - bird - complain" .)