| Term | Definition |
| fid | faith; trust |
| affidavit | sworn written statement made before an authorized official |
| bona fide | made or carried out in good faith; genuine |
| confidant | one to whom secrets are entrusted |
| confident | having faith in oneself; self-reliant; sure |
| confidential | communicated in trust; secret; private |
| diffident | lacking faith in oneself; timid; shy |
| fidelity | faithfulness to a trust or vow; accuracy; faithfulness of sound reproduction |
| fiduciary | held in trust; confidential |
| infidel | one who does not accept a particular faith; unbeliever |
| perfidious | false to a trust; faithless |
| perfidy | violation of a trust; treachery; faithlessness; disloyalty |