"Mug up" is a colloquial phrasal verb that means "to study or review intensively." There are several synonyms for this term, depending on the context. One possible synonym is "cram," which implies a last-minute, quick and intense study session, often to prepare for an exam or test. Another synonym is "swot up," which is more commonly used in British English and suggests a thorough and detailed review of a subject. "Bone up," "grind," "drill," and "hit the books" are also useful synonyms for "mug up," all emphasizing the idea of intensive and focused studying. Whatever synonym you choose, the key is to approach your studies with dedication and discipline.