Fides.
The Latin word for believe is credo, credere. We get the word "credit" from it.
Fides is the Latin word for faith, fide would be the ablative case, meaning "by faith"
fide in Latin means faith--- as in Bona Fide (in good faith) Confide (discuss with faith/trust), Fidelity (faithful devotion to on another).
Fides.
Habe fidem.
The words keep the faith in the Latin language are said as permanerent in fide. In the Italian language these words are mantenere la fede.
The Latin root of "fidelity" is fides, trust, belief, faith.
The Latin phrase for bad faith is mala fides. The Spanish phrase for these words is mala fe and the Italian phrase is malafede.
Fides (genitive: fidei, f).
Latin - 'in good faith'.
Fides et amor.