People who work together in the same workplace or on the same job or project.
From 'co-' (Latin prefix meaning together) + 'worker' (one who works). This is a modern compound that became standard in the 20th century with industrial and office work.
The term 'coworkers' is relatively recent—before the Industrial Revolution, people mostly worked in families or guilds, so you wouldn't have needed a word for 'people working in the same factory'—it's a linguistic artifact of mass employment.
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