Like its linguistic forerunners, the modern term didactic has more than one application. It can mean "designed or intended to teach" and "intended to convey instruction and information as well as pleasure and entertainment." Didactic also has particular applications to literature and other art, describing exercises used for improving skills as well as explanatory material. Didactic can be used to describe something involving lecture and textbook instruction rather than demonstration and laboratory study. It's easy to see how those senses led to the additional shadings "pompously dull and erudite" and "making moral observations." Another word with classical roots, pedantic, comes from the Latin verb meaning "to instruct" but carries stronger negative connotations: "narrowly, stodgily, and often ostentatiously learned" and "unimaginative, pedestrian."