Tolerant according to the letter (10)
I believe the answer is:
permissive
'tolerant' is the definition.
(thesaurus)
'according to the letter' is the wordplay.
'according to' becomes 'per' (I've seen this before).
'the letter' becomes 'missive' ('missive' can be a synonym of 'letter').
'per'+'missive'='PERMISSIVE'
(Other definitions for permissive that I've seen before include "Free" , "granting authorisation" , "Like our society" , "Showing indulgence" , "Lenient, indulgent" .)