长 (long) + 舌 (tongue) + 妇 (woman) = a woman with a 'long tongue' — i.e., someone whose tongue is always wagging. A vivid image of non-stop talking.
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This is a mildly derogatory term. While commonly used, it carries a sexist connotation as it specifically targets women. The gender-neutral 八卦的人 or 爱嚼舌根的人 can be used instead.
