sex·to·dec·i·mo /ˌsɛkstəˈdɛsəˌmo/
  十六開本,十六開紙
  Sex·to·dec·i·mo a.  Having sixteen leaves to a sheet; of, or equal to, the size of one fold of a sheet of printing paper when folded so as to make sixteen leaves, or thirty-two pages; as, a sextodecimo volume.
  Sex·to·dec·imo, n.; pl. Sextodecimos  A book composed of sheets each of which is folded into sixteen leaves; hence, indicating, more or less definitely, a size of a book; -- usually written 16mo, or 16°.
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