Other forms: gangbusters
If you had a gangbuster week at school, you aced all your tests and assignments. Gangbuster is also a noun referring to something really popular or successful: your new recipe for blueberry broccoli muffins could be a gangbuster! But probably not.
Gangbuster is a good example of a word with a very specific original meaning that has been extended or broadened to become more general. It was originally a noun referring to a police officer who broke up gangs and brought them to justice, especially in a spectacular or impressive way that made headlines. From that historical sense it was a short jump to the modern sense of "a spectacular success" — and from there to an adjective describing anything extremely successful.