An open-air automobile with two seats and no roof, popular in the early 1900s; can also mean a horse suitable for riding on roads.
From 'road' plus the agent suffix '-ster.' Originally described horses used for travel, then applied to the early sporty cars that resembled them in being open to the elements.
Early roadsters had no roofs because cars were still so slow and unreliable that people didn't want to be trapped inside during breakdowns! Open-air design was actually practical, not just stylish.
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