NeonKaos
Custodian
Dom.
Dominus.
Master.
Yeah, I knew about "Master" but I think "Dominus" was the word I was looking for. I needed the root word to be "Dom[whatever]" - the etymological "correct" form, not the BDSM-community "correct" form.
Anyway, I used the word "Dom" and it worked for the purposes intended.