Something that spins or turns around, or a part of your shoulder made of muscles and tendons that help your arm move in circles.
From Latin 'rotare' meaning 'to turn' plus the agent suffix '-or'. The shoulder meaning became common in medical terminology in the 20th century as doctors named anatomical structures.
Your rotator cuff is named like a machine part because it literally rotates your arm—but it's also one of the most injured parts of the body because we ask it to do impossible things, like throw a baseball at 90 mph!
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