I. Why Is This Sacrament Called “Orders”?

From The Catechism of the Catholic Church

1537
The word order in Roman antiquity designated an established civil body,
especially a governing body. Ordinatio means incorporation into an ordo. In the
Church there are established bodies which Tradition, not without a basis in
Sacred Scripture,⁴ has since ancient times called taxeis (Greek) or
ordines. and so the liturgy speaks of the ordo episcoporum, the ordo
presbyterorum, the ordo diaconorum. Other groups also receive this name of
ordo: catechumens, virgins, spouses, widows,….

PART TWO: THE CELEBRATION OF THE CHRISTIAN MYSTERY

SECTION TWO THE SEVEN SACRAMENTS OF THE CHURCH
- CHAPTER THREE THE SACRAMENTS AT THE SERVICE OF COMMUNION
  - ARTICLE 6 THE SACRAMENT OF HOLY ORDERS
    - I. Why Is This Sacrament Called “Orders”?

From The Catechism of the Catholic Church – rosary.team