Complain to terrible liar (4)
I believe the answer is:
rail
'complain' is the definition.
(I know that rail is a more specific form of the action complain)
'terrible liar' is the wordplay.
'terrible' indicates an anagram.
'liar' anagrammed gives 'RAIL'.
'to' is the link.
(Other definitions for rail that I've seen before include "Complain strongly or part of fence" , "Complain about - marsh bird" , "Means of transport" , "Bird with long legs" , "Water bird; bar" .)