Surrounded by leading academics sending up dull characters (4)
I believe the answer is:
amid
'surrounded by' is the definition.
(amid means among or surrounded by)
'leading academics sending up dull characters' is the wordplay.
'leading' says to take the initial letters (the leading letter of the word).
'sending up' shows that the letters should be reversed in order (in a down clue, letters go up).
'dull characters' becomes 'dim' (I can't justify this - if you can you should believe this answer much more).
The first letter of 'academics' is 'a'.
'dim' reversed gives 'mid'.
'a'+'mid'='AMID'
Can you help me to learn more?
(Other definitions for amid that I've seen before include "Within" , "Amongst" , "In the thick of" , "In the middle of" , "A dim sort of preposition" .)