The term 'IT IS SO' can be completed with the crossword solutions YES (3 letters), AMEN (4 letters), TRUE (4 letters), and FACT (4 letters). YES is an affirmative answer to a question or statement, while AMEN is a Hebrew word used to express agreement or acceptance. TRUE is an adjective meaning in accordance with FACT or reality, and FACT is a piece of information that is TRUE and can be verified. Together, these words indicate agreement and confirmation of a statement.