Everything you say is never wrong (8)
I believe the answer is:
universe
'everything' is the definition.
(everything in the universe)
'you say is never wrong' is the wordplay.
'you say' becomes 'u' ('you' as it sounds).
'wrong' is an anagram indicator.
'is'+'never'='isnever'
'isnever' is an anagram of 'niverse'.
'u'+'niverse'='UNIVERSE'
(Other definitions for universe that I've seen before include "Everything that exists anywhere" , "Everything, really" , "The earth and all the heavenly bodies" , "The whole of creation" , "The whole world" .)