Webster's Revised Unabridged Dictionary · 1913

dingdong

dingdong , noun

[See Ding.]

1.
The sound of, or as of, repeated strokes on a metallic body, as a bell; a repeated and monotonous sound.
2.
(Horology) An attachment to a clock by which the quarter hours are struck upon bells of different tones.
3.
a stupid or foolish person; -- used in a deprecatory or contemptuous sense. [slang]

Also: ding-dong