Dope stashed in a hollow cavity in bureau (6)
I believe the answer is:
agency
'bureau' is the definition.
(synonyms)
'dope stashed in a hollow cavity' is the wordplay.
'dope' becomes 'gen' (both can mean information).
'stashed in' means one lot of letters goes inside another.
'hollow' says to hollow out the word (remove centre letters).
'cavity' with its middle taken out is 'cy'.
'a'+'cy'='acy'
'gen' placed inside 'acy' is 'AGENCY'.
'in' is the link.
(Other definitions for agency that I've seen before include "Business that conducts business on behalf of another" , "Business that conducts business on behalf of others" , "Employment bureau" , "Travel ..., advertising..., employment" , "Government office" .)