Ogham
Ceirt is the letter whose meaning came apart underneath it. The word once meant a bush, collapsed into ceirt, a rag, and the later tree-list assigned it the apple to cover the gap. What the letter carries now is that slippage itself. Look today at something you are still doing for a reason that has quietly stopped applying. The habit is perfectly intact and the sense under it has gone. You are allowed to stop without having a replacement ready.