sophism (n.)

"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]

1680s, "student in the second year of university study," literally "arguer," altered from sophumer (1650s), from sophume, an archaic variant form of sophism, ultimately from Greek sophistēs "a master of one's craft; a wise or prudent man, one clever in matters of daily life."

The modern form probably is by folk etymology derivation from Greek sophos "wise" + mōros "foolish, dull" (see moron).

The original reference of the "arguer" name might be to the dialectic exercises that formed a large part of education in the middle years. At Oxford and Cambridge, a sophister (from sophist with spurious -er as in philosopher) was a second- or third-year student (what Americans would call a "junior" might be a senior sophister).