Probe fashionable expedition (7)
I believe the answer is:
inquest
'probe' is the definition.
(thesaurus)
'fashionable expedition' is the wordplay.
'fashionable' becomes 'in' (in can mean fashionable or trendy).
'expedition' becomes 'quest' (I've seen this in other clues).
'in'+'quest'='INQUEST'
(Other definitions for inquest that I've seen before include "Judicial enquiry" , "What-went-wrong investigation" , "hearing" , "Coroner's court" , "Inquiry into the cause of unexpected death" .)