sententious \sen-TEN-shuhs, adjective:

1. Abounding in pithy aphorisms or maxims: a sententious book.
2. Given to excessive moralizing; self-righteous.
3. Given to or using pithy sayings or maxims: a sententious poet.
4. Of the nature of a maxim; pithy.

For he was a poet and drowned untimely, and his verse, mild as it is and formal and sententious, sends forth still a frail fluty sound like that of a piano organ played in some back street resignedly by an old Italian organ-grinder in a corduroy jacket.
— Virginia Woolf, “Street Haunting: A London Adventure,” Collected Essays

It was inconceivable that she was using the boring, sententious, contentious Shepherd for anything but a hollow threat to him, but this semblance of wrongdoing could now be turned to advantage.
— Kurt Vonnegut, Player Piano

Sententious is related to sententia, the Latin root for the word sentence. The Latin word sententiosus meant “full of meaning, pithy.”