LATIN DICTIONARYLexicon Latīnum

fidē1

fidē (+ genitive)
Classical[ˈfɪ.deː]Ecclesiastical[ˈfiː.de]

Meaning

  1. with genitivein faith of, believing in
    indicii fide parum plene discussa380 CE – 392 CE, Ammianus Marcellinus, Res Gestae 28.1.56
adverb
fīdē2
fīdē (comparative fīdius, superlative fīdissimē)
Classical[ˈfiː.deː]Ecclesiastical[ˈfiː.de]

Meaning

  1. faithfully

Lewis & Short A Latin Dictionary, 1879

fīdē, adv.,
I. faithfully, v. fidus fin.

Origins

From fīdus + -ē.