Irony, defined.

On this balmy January morning in New England, (FYI: "balmy" means it was 26 degrees since that felt like "spring" compared to the minus 4 we've had) I was on my way to start the car and examine the trench my son dug in our front yard. We were talking about the process of using something to remember something else. All I could think of was "acronym" and while I know that an acronym can be this "thing," I could not remember the term itself: mnemonic device.