The term 'Say It's So' can be broken down into four crossword solutions: AVER (4 letters), ALLEGE (6 letters), ASSERT (6 letters), and AVOW (4 letters). AVER is a verb meaning to state something as a fact, often without providing proof. ALLEGE is also a verb, meaning to make a claim or accusation without providing proof. ASSERT is a verb meaning to state something confidently and forcefully. Finally, AVOW is a verb meaning to declare something openly and firmly. All four words can be used to express the idea of 'Say It's So, ' which is to declare something to be true.