Not choppy (4)
I believe the answer is:
calm
'not choppy' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for calm that I've seen before include "Peaceful, not excited" , "Halcyon" , "Still or peaceful" , "stained-glass window maker could need this" , "Still - force 0 on the Beaufort scale" .)