The Greek noun Hebraïs (Ἑβραΐς) means 'the Hebrew language' or more precisely 'the Hebrew/Aramaic dialect' spoken in first-century Palestine. It appears in Acts 21:40, 22:2, and 26:14, describing Paul speaking to crowds or hearing the voice of Christ in the Hebrew language/dialect.
The significance of Paul speaking 'in the Hebrew dialect' (Acts 21:40) is that the crowd fell silent — it commanded immediate attention and respect. For diaspora Jews, hearing their ancestral sacred language from a Roman citizen being arrested was startling. On the Damascus road, the risen Christ spoke to Paul 'in Aramaic/Hebrew' (Acts 26:14), the intimate language of covenant. God's self-revelation consistently meets people in their own language (Acts 2:11 — Pentecost) — a principle that drives all Bible translation. The language of God's speech is not merely functional; it carries covenantal, cultural, and personal weight.