To blur is to make something unclear or hard to see, as if it were smeared or out of focus. It can also mean to make the difference between two things less clear.
It likely comes from Middle English “blerren,” meaning “to dim the eyes,” perhaps imitating the sound of confused speech or crying. The sense of visual and mental confusion has always been central.
We talk about “blurring the line” between work and home, using a vision word for a lifestyle problem. English often uses eyesight as a metaphor for understanding: clear equals knowable, blurred equals confusing.
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