• Webster's Revised Unabridged Dictionary
    • a Pentatomic (Chem) Having five atoms in the molecule.
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Century Dictionary and Cyclopedia
    • pentatomic Containing in a single molecule five atoms altogether of the same or of different elements, as stannic chlorid, SnCl4; or, containing in a single molecule five atoms of some one element, as a pentose, which is an aldehyde alcohol or a ketone-alcohol containing five atoms of carbon. Frequently used in the same sense as quinquevalent.
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Webster's Revised Unabridged Dictionary
Penta-, + atomic,