If you and your brother are very different from each other — he's tall and you're short, he's studious and you're adventurous, he likes chocolate ice cream while you prefer vanilla — the two of you are unalike.
When you take apart unalike, you get un-, "not," and alike, "very similar to each other." So if you're wearing a formal gown and your oldest sneakers, the elements of your outfit are unalike. If your dad always votes Republican but your mom is a lifelong Democrat, they're unalike — politically, anyway. Use this adjective when you're talking about two or more things (or people) who are dissimilar or mismatched.