c. 1400, "to enter into negotiations," especially "discuss or arrange peace terms;" also "to treat (someone) in a certain way," from Anglo-French entretier, Old French entraiter "to treat," from en- "make" (see en- (1)) + traiter "to treat" (see treat (v.)). Meaning "to beseech, implore, plead with (someone)" is from early 15c.; meaning "to plead for (someone)" is from mid-15c. Related: Entreated; entreating.
noun suffix, in army, city, country, etc., from Old French -e, Latin -atus, -atum, past participle suffix of certain verbs, which in French came to be used to indicate "employment, office, dignity" (as in duché, clergié).
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Harper, D. (n.d.). Etymology of entreaty. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/entreaty