Bush-league is a slang term that refers to something that is amateur or unprofessional. The word is often used to describe a poor-quality performance or a substandard product. Some antonyms for the word 'bush-league' are expert, professional, first-class, top-notch, and masterful. If something is described as expert, it means it is done by an experienced and highly skilled person who knows how to do it right. Similarly, a professional product or performance is of the highest quality and meets the standard. On the other hand, top-notch and masterful imply excellence and proficiency in a particular field or activity. So, these are some antonyms for the word 'bush-league' that convey the opposite meaning.