All certain it's conducive to health (9)
I believe the answer is:
wholesome
'all' is the definition.
(thesaurus)
'certain it's conducive to health' is the wordplay.
I cannot quite understand how this works, but
'certain' could be 'some' (synonyms) and 'some' is located in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for wholesome that I've seen before include "Healthy in body, taste or morals" , "Good for you!" , "Moral" , "Respectable" , "Previously propitious" .)