Κύριε, βοήθησον τὸν δοῦλον σου Νῖλον κτλ. → Lord, help your slave Nilos ... (mosaic inscription from 4th-cent. church in the Negev)
P. and V. πιστός, V. κεδνός.
trustworthy: P. ἀξιόπιστος, P. and V. βέβαιος.
keeping one's oath: P. and V. εὔορκος.