In a way that shows concern for others' well-being rather than your own benefit.
From altruistic (19th century, from French altruisme), which comes from Latin alter (other) combined with the suffix -ism. The concept was formalized by Auguste Comte to describe unselfish concern for others.
Altruism is so recent as a formal concept that it's younger than photography! Before the 1800s, European languages didn't really have a single word for the idea of pure selflessness—they just said 'charity' or 'Christian virtue.'
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