Backtrack mendacious person? (4)
I believe the answer is:
liar
'person?' is the definition.
(liar is a kind of person)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for liar that I've seen before include "Tale-teller" , "Teller of fibs" , "Not a truth-sayer!" , "Fibber" , "one trying to sell pork pies" .)