First recorded in the Records of the Grand Historian (《史记·周本纪》) describing how the people "sang of [Hou Ji's] merit and praised his virtue" (民皆歌乐之，颂其德). Originally sincere; modern usage is almost always sarcastic.
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Strongly negative connotation today - calling someone's writing or speech 歌功颂德 means it's slavish flattery, especially toward those in power. Stock phrase in political and literary criticism.
