Lewis & Short

2. nixus, ūs, m. [1. nitor], a pressure (the same as nisus, v. 2, nisus).

  1. I. Lit.: astra se nixu suo conglobata continent, revolution, course, * Cic. N. D. 2, 46, 117.
  2. II. Transf., a striving, exertion, effort: hic ad summum non pervenit nixu (al. nisu), sed impetu, Quint. 8, 4, 9; 1, 12, 10.
    1. B. In partic., pains, throes, travail of parturition: fetūs nixibus edunt, Verg. G. 4, 199; Ov. H. 4, 126: laboriosi nixūs, Gell. 12, 1, 4.
  3. III. Nixus, a constellation; v. Engonasi.