Lewis & Short

1. fīdus, a, um, adj. [fido, that one may rely on], trusty, truslworthy, faithful, sure (class.).

  1. I. Prop., constr. absol., with dat., poet. also with gen.
    1. A. Absol.: nihil est stabile quod infidumNeque enim fidum potest esse multiplex ingenium et tortuosum, Cic. Lael. 18, 65; cf.: (amico) probo et fideli et fido et cum magna fide, Plaut. Trin. 4, 4, 4: tum se intellexisse, quos fidos amicos habuisset, quos infidos, Cic. Lael. 15, 53: amici, Hor. Ep. 1, 5, 24: sodales, id. S. 2, 1, 30: fidissima atque optima uxor, Cic. Fam. 14, 4, 6: conjux, Hor. Ep. 2, 1, 142: bonus atque fidus judex, impartial, id. C. 4, 9, 40: medici, id. Ep. 1, 8, 9: interpres, id. A. P. 133: fidiora haec genera hominum fore ratus, Liv. 40, 3, 4: nihil fidum, nihil exploratum habere, Cic. Lael. 26, 97: familiaritates fidae, id. Off. 2, 8, 30: canum tam fida custodia, id. N. D. 2, 63, 158: vis canum, Lucr. 6, 1222; cf.: pectus canum, id. 5, 864: pectus, Hor. C. 2, 12, 16: fido animo, firm, steadfast, Liv. 25, 15, 13.
    2. B. With dat.: (servum) quem domino fidissimum credebat, Liv. 33, 28, 13 (but cf.: fidus est amicus, fidelis servus, Don. Ter. Phorm. 1, 2, 26): quae fida fuit nulli, Tib. 1, 6, 77: nec tibi fidam promittis Lacaenam, Ov. H. 5, 99: ne quid usquam fidum proditori esset, no faith should be kept with a traitor, Liv. 1, 11, 7: ut eos sibi fidiores redderet, Just. 16, 5, 2.
    3. C. Poet. with gen.: regina tui fidissima, most faithful towards you, Verg. A. 12, 659; and with gen. partit.: juvenum fidos, lectissima bello Corpora, sollicitat pretio, the trusty ones, trustiest of the youth, Stat. Th. 2, 483.
    4. D. With in or ad, and acc.: in amicos fidissimus, Eutr. 7, 8: fidi ad bella duces, Nemes. Cyn. 82.
    5. E. With in and abl.: sperabam te mihi fidum in hoc nostro amore fore, Cat. 91, 1 sq.
  2. II. Transf., objectively of inanim. and abstr. things, sure, certain, safe, trustworthy (mostly poet. and in post-Aug. prose; in Cic. Att. 9, 6, 10, fuga fida is not critically certain; v. Orell. N. cr. ad loc.).
    1. A. Absol.: aures, Ov. M. 10, 382: spes fidissima Teucrum, Verg. A. 2, 281: ensis, trusty, id. ib. 6, 524: alii litora cursu fida petunt, id. ib. 2, 400: nec unquam satis fida potentia, ubi nimia est, Tac. H. 2, 92: pons validus et fidus, id. A. 15, 15 fin.: male fidas provincias, id. H. 1, 52.
    2. B. With dat.: (oppidum) naviganti celerrimum fidissimumque appulsu, Tac. A. 3, 1; cf.: statio male fida carinis, Verg. A. 2, 23: montem tantos inter ardores opacum et fidum nivibus, Tac. H. 5, 6.
      Sup.: nox arcanis fidissima, Ov. M. 7, 192: camelino (genitali) arcus intendere, orientis populis fidissimum, the surest, Plin. 11, 49, 109, § 261: refugium, Tac. A. 5, 8.
      Hence, adv.: fīde, faithfully, trustily (perh. only in the sup.): quae mihi a te ad timorem fidissime atque amantissime proponuntur, Cic. Fam. 2, 16, 4 (al. fidelissime): fidissime amicissimeque vixerunt, Gell. 12, 8, 6.

2. fīdus = foedus, a league, v. 2. foedus init.