Phil - 3d is indeed convoluted. I get the first letter sequence but find it clunky rather than clever, and assume that the first word is the definition.
The other point to make is that ON is the official abbreviation for Ontario, not ONT.
Replying to all so late in the day, been driving. Really enjoyed todays after being stuck for a bit . Brendan's post 7 noting the connection between 1a and 26a got me moving. Loved 25 a for my CoD. Can we get an insight into some abbreviations used by some. FOI for example.