Noun has 1 sense

• groundbreaking(n = noun.act) groundbreaking ceremony - the ceremonial breaking of the ground to formally begin a construction project;

Adjective has 1 sense

• groundbreaking(s = adj.all) innovational, innovative - being or producing something like nothing done or experienced or created before; "a mind so innovational, so original"; "innovative members of the artistic community"; "stylistically innovative works"