The Greek ordinal adjective pentekaidekatos means the fifteenth — the ordinal form of fifteen. It appears once in the New Testament in Luke's precise historical anchoring of John the Baptist's ministry.
Pentekaidekatos appears in Luke 3:1 — 'In the fifteenth year of the reign of Tiberius Caesar...' This verse is one of the most significant historical synchronizations in the New Testament. Luke, the careful historian, anchors the beginning of John's ministry to a specific, verifiable year in world history. The incarnation and the ministry that heralded it did not happen 'once upon a time' in a mythological space; they happened in a datable, verifiable historical moment. The 'fifteenth year' matters because the gospel is not timeless mythology but timely history — God acts in real, measurable time. The Word became flesh in a specific year, under a specific emperor, in a specific province. Faith is not irrational; it is anchored to historical events that can be examined.