Groundbreaking vs. ground breaking vs. ground-breaking

Here’s an old grammar controversy that’s easy to deconstruct.

The older you are, the more likely your junior high school teacher pounded into you that ground breaking and ground-breaking were the correct spellings when referring to the start of a construction project. These days, however, groundbreaking is far more prevalent, and both Merriam-Webster and Oxford Dictionaries consider it the correct spelling. This is the same spelling that’s used for the traditional definition of the word meaning “new and revolutionary” as in The scientist’s proposed theory was groundbreaking.

Ground breaking is still used, though its meaning generally is more literal, as in actually cracking the ground open, like Thor smashed his hammer in a ground breaking smash.