infiel
/inˈfjel/ · B2 · adj
unfaithful
💔 in + fiel = not faithful; fiel is Spanish for faithful, like English fidelity
From Latin infidelis: in- (not) + fidelis (faithful), the root of English fidelity and infidel. Spanish shortened fidelis to fiel, so infiel is simply not-fiel: an unfaithful partner, or a non-believer.