Other forms: groundbreakings; groundbreakingly
Something groundbreaking is brand new, important, and original, like groundbreaking research that proves your cat really does love you.
As a noun, groundbreaking is the traditional way of marking the very first day of a building project, when the ground is officially "broken," either literally with a shovel or figuratively. You could even attend the groundbreaking of a groundbreaking new hotel that's heated and cooled with sustainable geothermal energy. This word comes from the phrase to break ground, originally used to describe both construction and planting crops.