Opposite of none (3)
I believe the answer is:
all
'opposite of none' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for all that I've seen before include "without exception" , "Every single one" , "The whole quantity" , "and 18: 'Sing through -- --' (carol)" , "SECOND PART OF 8" .)