I'd nominate "casual" and "cadaver". The Latin cadō root had multiple meanings, like "fall", "die" and "decay". So while "cadaver" is obvious, "casual" took a

I'd nominate "casual" and "cadaver". The Latin cadō root had multiple meanings, like "fall", "die" and "decay". So while "cadaver" is obvious, "casual" took a circuitous route of "fall" -> "accident" -> "by chance", and eventually "informal".