Automobile designers in the 1930s began using elements of aircraft aerodynamics to smooth out the boxy-looking vehicles of their day.[9] Some designs that were ahead of their time when exhibited during the early 1930s included "teardrop" streamlining of the car's rear; a configuration similar to what would become known as 'fastback' 25 years later."[10] 'Fastback' was first recognized as a definition by Merriam-Webster in 1954,[full citation needed] many years before the term 'hatchback' was popularized and entered the dictionary in 1970.[11] Opinions vary as to whether the terms are mutually exclusive.