"Surething" is a popular expression that means something that is guaranteed to happen or be successful. There are many synonyms for this word that can be used depending on the context. In formal or professional settings, phrases like "assured" or "certain" can be used to convey the same meaning. In a more casual setting, words like "slam-dunk," "in-the-bag," or "a shoo-in" can be used. These words can be used to express confidence in an outcome or decision. Ultimately, the use of synonyms is a great way to add variety and nuance to your language and convey your message with precision.