Lewis & Short

dĕcussis, is (also decus, i, a mutilated form used by the Agrimensores, p. 231, 243, and 265, ed. Goes.), m. [decem-as].

  1. I. The number ten: ex singularibus rebus, quae μονάδες apud Graecos dicuntur perficitur decussis, Vitr. 3, 1 (cf. the art. as, no. I.).
    Hence, * decussis sexis, or in one word, dĕcussissexis, the number sixteen, Vitr. 3, 1, 8.
    1. B. Because the Roman numeral sign for ten was X, decussis was used to denote the intersection of two lines in the form of a cross: regula figitur in primo decussis puncto, Vitr. 10, 11; Plin. 18, 34, 77, § 331. Cf. decusso and its derivatives.
  2. II. (Acc. to as, no. II.) Ten asses; as a Roman coin, a ten-as piece, Varr. L. L. 5, § 170; Lucil. ib. 9, § 81 Müll.; Stat. Silv. 4, 9, 9; Fest. p. 237, 20 Müll.