"one who makes use of fallacious arguments," mid-15c., earlier sophister (late 14c.), from Latin sophista, sophistes, from Greek sophistes "a master of one's craft; a wise or prudent man, one clever in matters of daily life," from sophizesthai "to become wise or learned," from sophos "skilled in a handicraft, cunning in one's craft; clever in matters of everyday life, shrewd; skilled in the sciences, learned; clever; too clever," of unknown origin. Greek sophistes came to mean "one who gives intellectual instruction for pay," and at Athens, contrasted with "philosopher," it became a term of contempt.
Sophists taught before the development of logic and grammar, when skill in reasoning and in disputation could not be accurately distinguished, and thus they came to attach great value to quibbles, which soon brought them into contempt. [Century Dictionary]
Ancient Greek teachers who were accused by some of their contemporaries (including Plato) of being more interested in winning arguments through crafty rhetoric than in pursuing truth.
Note: By extension, a “sophist” is someone who engages in persuasive but false arguments.