Anne Curzan in the Lingua Franca blog, 'It's all downhill from here':
"A friend of mine’s daughter spotted a (semi-) auto-antonym — a word that has two opposing meanings — that was not on my radar: downhill. As she pointed out, the word can be positive when we use it metaphorically to refer to something getting easier from this point forward, and it can be very not positive when we use it metaphorically to refer to something (or everything!) getting worse from this point forward. It’s clearly not a perfect auto-antonym in that the meanings are not exactly semantic opposites (easier vs. worse), but it’s not outside the ballpark."