Ancient books devoured by a son in retreat where philosophers gathered (4)
I believe the answer is:
stoa
'where philosophers gathered' is the definition.
The definition suggests a singular noun which matches the answer.
'ancient books devoured by a son in retreat' is the wordplay.
'ancient books' becomes 'OT' (Old Testament).
'devoured by' indicates putting letters inside.
'son' becomes 's' (genealogical abbreviation for son).
'in retreat' shows that the letters should be reversed in order.
'a'+'s'='as'
'ot' inserted within 'as' is 'aots'.
'aots' back-to-front is 'STOA'.
Can you help me to learn more?
(Other definitions for stoa that I've seen before include "In Athens some columns" , "Series of columns covered" , "Portico or roofed colonnade" , "Make a Greek porch out of oats" , "old school" .)