One who's stopped lying about knight from the east (5)
I believe the answer is:
riser
'one who's stopped lying' is the definition.
'about knight from the east' is the wordplay.
'about' becomes 're' (regarding**).
'knight' becomes 'sir' (I've seen this before).
'from the east' says the letters should be written in reverse.
're'+'sir'='resir'
'resir' backwards is 'RISER'.
(Other definitions for riser that I've seen before include "One getting up" , "Front of a step; vertical pipe" , "Upright piece between steps" , "Vertical piece between two stair treads" , "Upright part of step - vertical pipe" .)