Lewis & Short

prīmordĭus, a, um, adj. [primus-ordior], original (post-Aug.): primordii seminis mistu, Col. 6, 37, 7 dub. (al. primordiis seminum).
Hence, as subst.: prīmor-dĭum, n., and more usually plur.: prī-mordĭa (gen. not in use; principiorum takes its place, Munro ad Lucr. 3, 262; separated and transposed, ordĭa prīma, Lucr. 4, 28), n.

  1. I. The first beginnings, origin, commencement (class.; syn.: principium, initium): primordia rerum, Cic. Part. 2, 7: a Jove Musarum primordia, id. poët. Leg. 2, 3, 7: mundi, Ov. M. 15, 67: gentis, Luc. 10, 177: veterum vocum, Pers. 6, 3: inquieta a primordiis vita, Sen. Brev. Vit. 6, 1: artis, Lact. 12, 10, 3: eloquentiae, Tac. Or. 12; Gell. 12, 1, 9; 17; Lact. 3, 29, 16; Just. 31, 5, 7: dicendi, Quint. 1, 9, 1: terrena, Col. 3, 10, 10: mundi, Sulp. Sev. Chron. 1, 4, 1: in primordiis, Pall. 4, 12.
    In sing.: a primordio urbis, Liv. init.; Col. 1, 1: in operum suorum primordio stare, in the first beginning, Curt. 9, 2, 11; Just. 2, 1: tam tenues primordio imperi fuere fines, Plin. 3, 5, 9, § 56.
  2. II. Absol., the beginning of a new reign, Tac. A. 1, 7.