If something is prosaic, it is ordinary and a bit dull — no spark, no poetry in it. A prosaic job might be filling in forms. A prosaic explanation is clear but lifeless. The word is not a shout of insult; it quietly says “this is plain, and a little boring.” You meet it in books and careful speech more than in chat. Though actually, it started as a word about writing. Prosaic first meant “in prose,” not in verse — straightforward language, as opposed to a poem. Over time the “not a poem” meaning slid into “not interesting.” Today almost nobody uses prosaic to mean “written in prose.” They use it to mean everyday and unimaginative. That slide is the messy truth: a word about a kind of writing became a word about a kind of feeling.