Experienced rabbi lies regularly (4)
I believe the answer is:
able
'experienced' is the definition.
(I've seen this in another clue)
'rabbi lies regularly' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'rabbi'+'lies'='rabbilies'
The alternate letters of 'rabbilies' are 'ABLE'.
(Other definitions for able that I've seen before include "showing talent" , "Capable seaman" , "Having the power, skill or means (to do something)" , "Bright" , "... was I ere I saw Elba (palindrome)" .)