πενθήμερος
From LSJ
Κύριε, βοήθησον τὸν δοῦλον σου Νῖλον κτλ. → Lord, help your slave Nilos ... (mosaic inscription from 4th-cent. church in the Negev)
English (LSJ)
ον,
A of five days, ἀγών Sch. Pi.O.5.13 ; κατὰ πενθήμερον for alternate periods of five days, X.HG 7.1.14 ; once in every five days, Arist.Ath.30.4 ; also καθ' ἑκάστην πενθήμερον SIG364.9 (Ephesus, iii B. C.).