Lewis & Short

dū̆plĭo, ōnis, m. [duplus],

  1. I. the double of any thing (very rare), XII. Tab. ap. Fest. S. V. VINDICIAE, p. 376, 30 Müll.; Plin. 18, 3, 3, § 12; cf. Paul. ex Fest. p. 66, 13 Müll.
  2. II. Esp., the double of the perfect number, six, i. e. twelve, = διπλασίων; cf. Vitr. 3, 1, 6.