Ministry of Abnegation
As stipulated by the Writ of Union, the Ministry of Abnegation was responsible for overseeing the Ascetics, a Sangheili order that was dissolved and reconstituted as a subordinate of the Ministry during the foundation of the Covenant.
Writ of Union
The Ministry of Abnegation was formed around the time the Writ of Union was formed. Under the terms of the Union the Ascetics were dissolved and reconstituted under the then-newly formed Ministry, where for centuries the Ascetics served.
Abnegation to deny or renounce something, which fits with the Asceticism's role of self-denial.