Double bell? (6)
I believe the answer is:
ringer
This clue is a double definition.
'double' is the first definition.
(I've seen this before)
'bell?' is the second definition.
(I've seen this in other clues)
(Other definitions for ringer that I've seen before include "match" , "Doppelganger" , "clanger?" , "bell" , "One calling" .)