Dull person in tunnel (4)
I believe the answer is:
bore
I believe this is a double definition.
'dull person' is the first definition.
(I've seen this in another clue)
'tunnel' is the second definition.
(I've seen this in another clue)
'in' is the link.
(Other definitions for bore that I've seen before include "Drill a hole in" , "Tedious person; steep wave" , "Dull person; hole" , "Irritate" , "hole > not something of interest" .)