A dibber is a
cylindrical device used to push down semi-solid material.
In
gardening, a dibber is about an inch wide, and used to push down soil, to make room for bulbs or seeds. At a push
1, the handle of a
trowel or one's
finger both make perfectly acceptible dibbers.
When hand-rolling a
cigarette or
joint, a small dibber is used to push down the material to allow a
filter or
roach to be inserted. Some
lighters have a removable
flint assembly that can be used as a dibber.
It is entirely possible that 'dibber' is a
chiefly British word (as
microsoft bookshelf is fond of saying).
1 - hoho.