Surrounded by thousand in support (4)
I believe the answer is:
'surrounded by' is the definition.
(I've seen this before)
'thousand in support' is the wordplay.
'thousand' becomes 'm' (synonyms).
'in' is an insertion indicator.
'support' becomes 'aid' (to aid is to help or support).
'm' placed within 'aid' is 'AMID'.
(Other definitions for amid that I've seen before include "A dim sort of preposition" , "Maid (anag)" , "In the centre of" , "In the course of" , "Among" .)