Lewis & Short

septŭāgēni, ae, a

    (
  1. I. gen. plur. septuagenarum, Cod. Th. 14, 4, 4, § 1), num. distrib. adj. [septuaginta], seventy each: pyramides in imo latae pedum quinum septuagenum, Plin. 36, 13, 19, § 92; for which, in one word, fistula septuagenumquinum, Front. Aquaed. 57; cf. sexageni.
  2. II. Seventy at a time, seventy: septuagies septuageni pedes, Col. 5, 2, 7.
    Sing., each seventieth: coitu, Plin. 26, 10, 63, § 99.