deontology

Etymology tree
Ancient Greek δέω (déō)
Ancient Greek δεῖ (deî)lbor.
Proto-Indo-European *leǵ-
Ancient Greek λόγος (lógos)
Proto-Indo-European *-éh₂
Proto-Indo-European *-i-eh₂
Ancient Greek -ῐ́ᾱ (-ĭ́ā)
Ancient Greek -λογῐ́ᾱ (-logĭ́ā)bor.
Latin -logialbor.
French -logiebor.
English -logy
English deontology
Learned borrowing from Ancient Greek δέον (déon, “that which is binding, needful, proper, or right”) + English -ology (variant of -logy (suffix denoting a branch of learning or a study of a particular subject)). Δέον (Déon) is the neuter present participle of δεῖ (deî, “it behoves one to, it is necessary to, one must”), from δέω (déō, “to bind, tie; to fasten; to fetter”), ultimately from Proto-Indo-European *deh₁- (“to bind”).
Sense 1 (“synonym of ethics”) was coined by the English philosopher Jeremy Bentham (1748–1832) to refer to censorial or dicastic ethics (ethics based on judgment), while sense 1.1 (“normative ethical theory that the morality of an action should be based on whether the action follows certain obligations or rules”) derives from the use of the word deontological by the English philosopher Charlie Dunbar Broad (1887–1971) in his book Five Types of Ethical Theory (1930).