'fide' originates from Latin, specifically the word 'fides', where the root 'fid-' meant 'trust, faith'.

'fides' in Classical Latin gave rise to Medieval/Church Latin and to derivatives such as Latin 'fidelitas' and Old French forms (e.g., 'fidelite'), and these in turn produced English words like 'fidelity' and elements seen as 'fide-'.

Initially, it meant 'trust' or 'faith' in Latin; over time it has remained semantically stable but is primarily used in English as a bound root or in fixed phrases rather than as a free common noun.