Lewis & Short

dē-certo, āvi, ātum, 1, v. n. and a., to go through a decisive contest, to fight it out (but certare, to fight, without reference to the result. But the difference was not strictly observed. Thus Caesar uses often —15 times—decertare, but never certare; Sallust only the latter; and Cicero the two indifferently; cf.: decerno, I. B. and no. II. inf.).

  1. I. In the milit. sphere.
          1. (α) With abl.: proelio decertare, Caes. B. C. 1, 50, 4; so id. ib. 7, 77, 8; id. B. C. 1, 81, 5; 3, 37; 44; cf.: proeliis cum acerrimis nationibus, Cic. Prov. Cons. 13, 33: pugnā, Caes. B. G. 3, 23, 7: cum civibus armis, id. B. C. 3, 19; so ferro in ultima, Ov. M. 14, 804: cornu cum mare (aries), id. F. 4, 101: manu, Cic. Off. 1, 23 fin.
          2. (β) Without abl.: ut (Pompeium) pari condicione belli secum decertare cogeret, Caes. B. C. 3, 78, 3; so cum toto exercitu, Hirt. B. G. 8, 7, 6: iterum paratum esse decertare, Caes. B. G. 1, 44, 9; so absol., id. ib. 2, 10; id. B. C. 2, 6; Tac. H. 2, 33 al.; Vulg. Johan. 18, 36: de salute omnium, Auct. B. Alex. 16, 3.
            Pass. impers.: cum duobus ducibus de imperio in Italia decertatum est, Cic. Lael. 8 fin.; Auct. B. Alex. 16, 6; Auct. B. Afr. 19 fin.
    1. B. Poet. like certo (v. h. v, no. I. fin.) as v. a., to fill with strife or contention, to fight for, to achieve by fighting, contending: regna profanis decertata odiis, Stat. Th. 1, 2: ventis decertata aequora, id. ib. 479: decertati labores, Claud. Laud. Stil. 1, 21; cf.: Artemisia certamen laudibus ejus dicundis facit … ad eas laudes decertandas venisse dicuntur viri, Gell. 10, 18, 5.
  2. II. Beyond the milit. sphere, to contend: erat non jure, non legibus, non disceptando decertandum; armis fuit dimicandum, Cic. Planc. 36: decertare contentione dicendi, to contend, to strive, to vie with one, id. Phil. 2, 1, 2; cf.: tanta contentione cum consulibus, id. Fam. 5, 8: and, inter se, id. Fin. 5, 2, 5: cum sint duo genera decertandi, unum per disceptationem, alterum per vim, Cic. Off. 1, 11, 34; in the gymnasium, ludicra virginum inter se decertantium, Mela, 1, 7, 4.
    1. * B. Poet. of inanimate subjects: Africus Decertans Aquilonibus, * Hor. Od. 1, 3, 13.