Where does “πεντηκοστύς” come from?

πεντηκοστύς (Ancient Greek) comes from Ancient Greek πεντηκοστός, from Ancient Greek πεντήκοντα, from Proto-Indo-European penkʷēḱomth₂, from Proto-Indo-European *pénkʷedḱomt.

Ancestry of “πεντηκοστύς”, step by step

StepLanguageWordMeaning
1Ancient Greekπεντηκοστόςfiftieth
2Ancient Greekπεντήκονταfifty
3Proto-Indo-Europeanpenkʷēḱomth₂
4Proto-Indo-European*pénkʷedḱomt
Every word from Proto-Indo-European *pénkʷedḱomtEvery word from Proto-Indo-European penkʷēḱomth₂Every word from Ancient Greek πεντήκοντα