"Fizz-nik" is a slang word with no real synonyms. It is often used to describe someone who is energetic, lively, or playful. However, there are a few words that could be used to describe someone with similar qualities. For example, "ebullient" means cheerful and full of energy, while "vivacious" means lively and spirited. "Bubbly" could also be used to describe someone who is effervescent and vivacious. Overall, while "fizz-nik" may not have a perfect synonym, there are many words that can be used to capture the same energetic and playful spirit.