Definition of duller
(of a person) slow to understand; stupid.
It was alleged that slower children were occasionally told to stay away from school on the inspection day and that some dull children were refused admittance to schools altogether.
lacking brightness, vividness, or sheen.
The bell on the door tinkled merrily in the dull glow of lamplight.
lacking interest or excitement.
It is a gifted novelist, indeed, who can make ordinary events come alive, and who can interest the reader in ordinary, even dull , characters.