Baptist

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Middle English (in baptist (sense 2)): from Old French baptiste, via ecclesiastical Latin from ecclesiastical Greek baptistēs, from baptizein ‘immerse, baptize’.

wiktionary

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From Middle English baptist, baptiste, borrowed from Old French baptiste, from Ecclesiastical Latin, Late Latin baptista, from Ancient Greek βαπτιστής(baptistḗs).

etymonline

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baptist (n.)

c. 1200, "one who baptizes," also (with capital B-) a title of John, the forerunner of Christ; see baptize + -ist. As "member of a Protestant sect that believes in adult baptism upon profession of faith," generally by full immersion (with capital B-), attested from 1654; their opponents called them anabaptists (see Anabaptist).