Ken say, key policy expert needing lift (9)
I believe the answer is:
knowledge
'ken' is the definition.
(thesaurus)
'say key policy expert needing lift' is the wordplay.
'say' becomes 'eg' (both can mean for example).
'key' becomes 'del' (del key on a keyboard).
'policy expert' becomes 'wonk' (I've seen this in another clue).
'needing lift' says the letters should be written backwards (in a down clue, letters go up).
'eg'+'del'+'wonk'='egdelwonk'
'egdelwonk' written backwards gives 'KNOWLEDGE'.
(Other definitions for knowledge that I've seen before include "Information; awareness" , "Cognition, wisdom" , "Information - erudition" , "An organised body of information" , "a small amount is risky" .)