Longest-serving member (4)
I believe the answer is:
dean
'longest-serving member' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dean that I've seen before include "Glos. forest; Dixie ---, Everton hero" , "Clergyman; narrow valley" , "One is in charge of a university department" , "Small valley - cathedral dignitary" , "A senior clergyman - Swift was one" .)