Lewis & Short

conjūrātĭo, ōnis, f. [conjuro], a swearing together.

  1. I. Prop.
    1. A. In gen.: conjuratio fit in tumultu, i. e. Italico bello et Gallico quando vicinum urbis periculum singulos jurare non patitur, Serv. ad Verg. A. 7, 615; cf. id. ib. 2, 157; 8, 1 and 5.
      Hence, transf., a union or alliance: quae haec est conjuratio! utin omnes mulieres eadem aeque studeant nolintque omnia, Ter. Hec. 2, 1, 1: urbana, Plin. Pan. 70 fin.
      1. 2. A levy en masse, an enlistment of the whole people (late Lat.), Serv. ad Verg. A. 7, 614; 8, 5.
    2. B. In a bad sense, a conspiracy, plot (in good prose; most freq. in the histt.), Cic. Cat. 2, 4, 6; Caes. B. G. 1, 2; Sall. C. 17, 1 et saep.: si omnia facienda sunt, quae amici velint: non amicitiae tales, sed conjurationes putandae sunt, Cic. Off. 3, 10, 44: convicti adversum se conjurationis, Eutr. 7, 21: conjuratio nefanda in omne facinus ac libidinem, Liv. 39, 38, 3.
  2. II. Meton. (abstr. pro concr.), the confederacy, the band of conspirators themselves: perditorum hominum, Cic. Cat. 1, 6, 13.