(rare, sometimes capitalized) A person who uses a great deal of jargon when speaking or writing, especially one who seems to relish such a manner of expression.
A friend of mine had a slight skin rash she couldn't identify, so she went to a real Jargoneer. He scowled at the rash, went "Hmmm" several times, then made a couple of sorties into his lab. . . . Finally he came back and informed her impressively that she was suffering from an Indeterminate Dermatitis.