Come to understand lies are naughty (7)
I believe the answer is:
realise
'come to understand' is the definition.
(I've seen this before)
'lies are naughty' is the wordplay.
'naughty' indicates anagramming the letters.
'lies'+'are'='liesare'
'liesare' with letters rearranged gives 'REALISE'.
(Other definitions for realise that I've seen before include "Grasp" , "Apprehend; see lair (anag.)" , "Comprehend and convert into money" , "Convert (asset) into cash" , "work out" .)