Note what’s coming on Sunday, right? Not once (5)
I believe the answer is:
never
'not once' is the definition.
(I've seen this before)
'note what's coming on sunday right?' is the wordplay.
'note' becomes 'n' (abbreviation).
'what's coming on sunday right?' becomes 'ever' (I can't justify this - if you can you should believe this answer much more).
'n'+'ever'='NEVER'
Can you help me to learn more?
(Other definitions for never that I've seen before include "Under no circumstances" , "' - - Say - - Again': Bond film" , "On no occasion" , "No way" , "when pigs fly" .)