(adjective)
in literary usage, drab, dull, or dark/dusky in appearance;
e.g. We could not see much in the dun light of the evening.
(adjective)
having a black mane and tail and a coat that is grayish-yellow in color, used to describe a horse;
e.g. He rode a dun horse to reach the station.
(noun)
a horse that has a black mane and tail and a grayish-yellow coat;
e.g. The dun was the fastest horse in the race.
(noun)
a mayfly that is not fully adult, or an artificial fly that is used as fishing bait due to its resemblance to a real insect;
e.g. He attached a dun to the end of his line and cast it into the water.
(noun)
an urgent demand for payment, or some other request;
e.g. He outlined his dun in a stern letter.
(noun)
in old usage, a person who is insistent in demanding that some payment be made, especially in collecting on debt payments;
e.g. She didn't want the dun to come knocking at their door.
(verb)
to pester someone or persistently make demands of them, especially for payment (usually to repay a debt);
e.g. They began to dun him for the money he had borrowed from them.