The prefixes of the words dissuade and persuade mean "against" and "thoroughly", respectively. So what does suade mean, and why don't we have it in English? There actually is a sort of obsolete word, suasion, which means the exact same thing as persuasion. It and the roots of the other two words go back to the Latin verb suadere, which meant "urge" or "recommend" (so dissuasion is recommending against something, while persuasion is thoroughly recommending in favor of it). Suadere derives from the Proto-Italic root swadeo, which is from the Proto-Indo-European root swehd, meaning "sweet" (also the etymon of sweet, along with words like hedonist, suave, and assuage). The idea was probably that the act of suasion required sweet-talking, or that the things being advocated for were often sweet.
Hello! I'm Adam Aleksic. This year, I graduated from Harvard University with a degree in Government and Linguistics. There, I co-founded the Harvard Undergraduate Linguistics Society and wrote a thesis on Serbo-Croatian language policy, magna cum laude. In addition to etymology, I also really enjoy philosophy, trivia, vexillology, geography, board games, conlanging, art history, and law.