Smith's Bible Dictionary
Onycha. Spoken of in Exodus 30:34, was one of the ingredients, of the sacred perfume. It consists of the shells of several kinds of mussels, which, when burned, emit a strong odor.
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Smith, William, Dr. Entry for 'Onycha'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/o/onycha.html. 1901.