Lewis & Short

nāvanter, adv., v. navo fin.

nāvo, āvi, ātum, 1, v. a. [navus], to do, perform, or accomplish a thing with zeal and diligence (class.): nemo est tam afflictus, quin possit navare aliquid et efficere, Cic. Fam. 6, 1, 7: navare operam alicui, to come to one’s assistance, to serve or assist one: utinam potuissem tibi operam meam studiumque navare, id. ib. 15, 12, 2: operam rei publicae, id. ib. 10, 25, 2; cf. id. Att. 1, 17, 4: jam mihi videor navāsse operam, quod huc venerim, to have succeeded in my endeavors, id. de Or. 2, 7, 26: fortiter in acie navare operam, to act vigorously, Liv. 7, 16; 28, 35: navandae operae avidior, Tac. A. 3, 42; for which: opus navare, Val. Fl. 3, 144: quam vellem Bruto studium tuum navare potuisses! to show, exhibit, Cic. Att. 15, 4, 5; cf.: si suffragandi studia non navant, id. Q. Cic. Petit. Cons. 5, 18: benevolentiam, id. Fam. 3, 10, 3: bellum, to prosecute vigorously, Tac. H. 3, 25: flagitium, to commit, perpetrate, id. ib. 4, 59: rem publicam, to serve the state, Cic. Fam. 9, 2, 5 (dub.; B. and K. gubernare).
Hence, adv.: nā-vanter, with zeal, Cassiod. Var. 2, 23 al.