/grownd"bray'king/ , n.
1. the act or ceremony of breaking ground for a new construction project.
adj.
2. of or pertaining to such a ceremony.
3. originating or pioneering a new endeavor, field of inquiry, or the like: Pasteur's groundbreaking work in bacteriology.
[ 1905-10; GROUND 1 + BREAK + -ING 1 , -ING 2 ]