The Greek noun euthytēs (εὐθύτης) means straightness, uprightness, rectitude, righteousness. It is derived from euthus (straight, right) and appears once in the NT — in Hebrews 1:8, quoting Psalm 45:6 (LXX). The term describes the moral quality of God's rule: it is not crooked, not biased, not corrupt — it is perfectly straight and right.
The Hebrews 1:8 quotation is a direct address to the Son: "Your throne, O God, is forever and ever, and the scepter of euthytēs is the scepter of your kingdom." The scepter was the symbol of royal authority; its straightness symbolizes the moral character of the reign it represents. Christ's kingdom is characterized by perfect rectitude — no favoritism, no corruption, no injustice. He has "loved righteousness and hated wickedness" (Heb 1:9). In a world of bent rulers and crooked systems, the reign of the Son is absolutely straight. This is the ground of hope for the oppressed and the standard for all who serve under His authority.