Was untruthful (4)
I believe the answer is:
lied
'was untruthful' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lied that I've seen before include "Idle (anag.)" , "Told stories" , "Stated falsely" , "Was untruthful; song" , "Produced pork pie" .)