Fool comes up with wise quotation (7)
I believe the answer is:
passage
'quotation' is the definition.
(thesaurus)
'fool comes up with wise' is the wordplay.
'fool' becomes 'sap' (synonyms).
'comes up' says the letters should be written backwards (in a down clue, letters go up).
'with wise' becomes 'sage' (similar in meaning. I am not sure about the 'with' bit.).
'sap' in reverse letter order is 'pas'.
'pas'+'sage'='PASSAGE'
Can you help me to learn more?
(Other definitions for passage that I've seen before include "Piece of text or music" , "Way through; sea journey" , "Corridor or narrow laneway" , "Some reading" , "equestrian manoeuvre" .)