Just as brief? Not these days! (2,6)
I believe the answer is:
no longer
'just' is the definition.
Both the answer and definition are adverbs. Perhaps you can see an association between them that I can't see?
'brief? not these days' is the wordplay.
'brief?' means to remove the last letter (a shorter or briefer version of the word).
'these days' becomes 'longer' (I can't explain this - if you can you should believe this answer much more).
'not' with its final letter removed is 'no'.
'no'+'longer'='NO LONGER'
'as' is the link.
Can you help me to learn more?
(Other definitions for no longer that I've seen before include "Not as formerly" , "a person without yearnings?" , "One not disposed to pining" , "Someone who doesn't dream" .)