What does "not least" mean here? Is it an idiom?
"Last but not least" is an idiomatic expression. It means that although some point was mentioned last, it is not least in importance. The rapper in this song is listing out the things he wants to do if he becomes a billionaire. He mentions "granting someone their last wish" at the end. By saying "last but not least," he is saying that although this point was mentioned last, that does not mean it is least important. Ex: I would like to thank my director, co-worker, and last but not least, my family. Ex: My family consists of my parents, siblings, and last but not least, my dog.