Here is a worksheet on the Greek word roots di and diplo. They mean two and double. You’ll find these roots underneath an everyday word like dilemma, but on this worksheet (which, if the book from which it is adapted is to be believed, contains words commonly found on the SAT), you’ll find it at the base of linguistic terms like digraph and diphthong, and scientific words like dichloride and dichromate.
If you find typos in this document, I would appreciate a notification. And, as always, if you find this material useful in your practice, I would be grateful to hear what you think of it. I seek your peer review.