A weight containing 480 g, or 1/12 pound troy and apothecaries' weight, or 437.5 g, 1/16 pound avoirdupois. The apothecary oz (used in the USP) contains 8 drams and is equivalent to 31.10349 g; the avoirdupois oz is equivalent to 28.35 g. [L. uncia, the twelfth part (of a pound or foot) hence also inch]
