* Break it down: Think of it as "mill" (like a thousand) + "ennium" (a period of time).
* Visualize it: Imagine a "mill" (a place where grain is ground) with a big "EN" sign over it.
* Rhyme it: "Millennium" rhymes with "phenomenon."
* Mnemonic: "M" for "many" years, "Ill" for "a thousand years," "En" for "end."
* Context: You'll likely only write it when referring to a thousand-year period, so the context might help you spell it correctly.
No matter which method you choose, the key is to find a way that makes sense to you and sticks in your memory!