(n.) One who, or that which, expounds or explains; an expounder; a commentator.

Boanerges allegorist annotator author book reviewer chalk talker cicerone clarifier commentator commenter critic cryptanalyst cryptographer cryptologist decoder definer demonstrator demythologizer descanter diaskeuast discourser disquisitor dragoman editor editorial writer editorialist emendator emender essayist euhemerist exegesist exegete exegetist explainer explicator exponent expounder glossarist glossographer go-between guide hermeneut homilist interpreter leader writer lecturer lexicographer metaphrast monographer monographist news analyst oneirocritic paraphrast praelector preacher publicist pulpitarian pulpiteer reader reviewer scholiast sermoner sermonist sermonizer textual critic tractation translator writer