The phrase "fifty-fifty" means an equal or even chance for both outcomes. Some synonyms for this phrase include equal split, half and half, even odds, balanced probability, and 50-50 shot. These phrases are commonly used in sports, gambling, and everyday conversations to describe a fair chance for both sides. Other expressions that mean the same thing are toss-up, coin toss, and head or tails. It's important to note that the use of these terms doesn't guarantee an even outcome, but it indicates that the chances are equal, and the outcome can be unpredictable.