The Ctistae (Greek: κτίσται) were a group/class in ancient Thracian culture. They led celibate lives, never marrying. They were held in a place of honor by the Thracians, with their lives being dedicated to the gods.
Etymology
The Bulgarian word чисти (chisti) can be used to explain the name of this ancient Thracian group. "chist" means clean/pure, and "chisti" is the plural form of the word, just like "ctistae" is the plural form of "ctist". It is possible that the letters ct (κτ) are simply a way of writing down the "ch" sound, not present in the ancient Greek alphabet.
References
Ctistae Wikipedia(Text) CC BY-SA