Sibyl supports these nuts inside (10)
I believe the answer is:
prophetess
'sibyl' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'supports these nuts inside' is the wordplay.
'supports' becomes 'props' (prop is a kind of support).
'nuts' indicates an anagram (nuts can mean crazy).
'inside' means one lot of letters goes inside another.
'these' with letters rearranged gives 'hetes'.
'props' enclosing 'hetes' is 'PROPHETESS'.
Can you help me to learn more?
(Other definitions for prophetess that I've seen before include "diviner" , "Forecaster" .)