To undo. Comes from the key code you type on a computer keyboard to undo something---hold down ctrl (which usually also has a little diamond on it) and Z.
I wish I could diamond Z last night... I never should've gone to that party
The Urban Dictionary Mug
One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids.
Buy the mug