tardiloquent
obs. rare
Speaking slowly, slow-speaking

in Reading the OED, Ammon Shea suggests, "In my estimation, there are only two possible reasons people speak slowly. Either they are not quite bright enough to get the words out any faster or they think you aren't quite bright enough to understand them any other way. In either case you're stuck in a conversation with someone who is tardiloquent, and something has gone horribly wrong."