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The Collaborative International Dictionary of English v.0.48 (gcide)

Blackboard \Black"board`\ (bl[a^]k"b[=o]rd`), n.
A broad board painted black, or any black surface on which
writing, drawing, or the working of mathematical problems can
be done with chalk or crayons. It is much used in schools. In
late 20th century similar boards of a green slate as well as
some colored white became common; wrioting on the slate
bioards may be done with chalk, but writing on the white
boards is done with colored pens, such as grease pens, which
leaves a trace that can be easily erased. The newer boards,
usualy called {chalkboards} are nevertheless still sometimes
referred to as blackboards.
[1913 Webster]