Python slid lengthways, to an extent (4)
I believe the answer is:
idle
'python' is the definition.
(Eric Idle, member of Monty Python)
'slid lengthways to an extent' is the wordplay.
'to an extent' indicates a hidden word.
'IDLE' is hidden within 'slid lengthways'.
(Other definitions for idle that I've seen before include "Inactive - lied (anag)" , "Unoccupied (time); run (engine) slowly" , "out of a job" , "Fruitless" , "Not in action or at work" .)