Groundbreaking is defined as something innovative, pioneering or that has never been done before.(adjective)
When there is a new medicine that may help to treat cancer that has never been in existence before, this is an example of a groundbreaking new treatment.
The definition of a groundbreaking is a ceremony held when construction is started on a new building.(noun)
An example of a groundbreaking is when the mayor comes before the media to dig up the first shovel full of dirt for the new police building.
See groundbreaking in Webster's New World College Dictionary
See groundbreaking in American Heritage Dictionary 4
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