To bring in social worker is significant (9)
I believe the answer is:
important
'significant' is the definition.
('important' can be a synonym of 'significant')
'to bring in social worker' is the wordplay.
'to bring in' becomes 'import' (I've seen this before).
'social worker' becomes 'ant' (I've seen this before).
'import'+'ant'='IMPORTANT'
'is' acts as a link.
(Other definitions for important that I've seen before include "Main" , "of great concern" , "Eminent" , "Meaningful" , "material" .)