Prove it! is a phrase used to challenge someone to demonstrate the truth of a statement or claim. The term can be broken down into three crossword solutions: THEOREM (7 letters), THESIS (6 letters), and Showme (6 letters). A THEOREM is a mathematical statement that has been proven to be true, while a THESIS is an argument or opinion that is supported by evidence. Showme is a phrase used to challenge someone to provide proof of a statement or claim.