The term "deontic" originates from Ancient Greek.
Ancient Greek Root: The word comes from the Ancient Greek noun δέον (déon), which means "that which is needful," "proper," or "duty."
In philosophy, and later in linguistics, "deontic" is used to describe aspects related to should, must, may, commanding, or forbidding. It essentially deals with norms, duties, and permissions.
Deontology itself, as a philosophical doctrine, is the ethics of duty. In deontology, the morality of an action is judged primarily by whether it conforms to certain rules or duties, regardless of its consequences.
The adjective "deontic" and the associated concept of "deontic modality" were established in the 20th century in logic and linguistics. This was done to distinguish this specific type of expressing necessity or possibility, which is based on norms or duties, from other modalities (like epistemic modality, which relates to knowledge and probability).
