Twice as tolerable (4)
I believe the answer is:
soso
'tolerable' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'twice as' is the wordplay.
'twice' shows that letters should be duplicated.
'as' becomes 'so' (I've seen this in other clues).
'so' duplicated is 'SOSO'.
Can you help me to learn more?
(Other definitions for soso that I've seen before include "Indifferent" , "mediocre" .)