Season in which lord keeps very quiet (6)
I believe the answer is:
pepper
'season' is the definition.
(thesaurus)
'lord keeps very quiet' is the wordplay.
'lord' becomes 'peer' (peer is a kind of lord).
'keeps' is an insertion indicator.
'very quiet' becomes 'pp'.
'peer' placed around 'pp' is 'PEPPER'.
'in which' acts as a link.
(Other definitions for pepper that I've seen before include "Pungent condiment" , "Pungent spice" , "Pungent seasoning and vegetable" , "Condiment or vegetable" , "Pelt" .)