The term 'proof word' is used in the printing industry to refer to a word or phrase that is printed on a proof copy of a document to ensure that the final version is accurate. The four crossword solutions for this term are ERAT (4 letters), STET (4 letters), ERGO (4 letters), and DELE (4 letters). ERAT is Latin for 'let it stand, ' STET is Latin for 'let it stand, ' ERGO is Latin for 'THEREFORE, ' and DELE is Latin for 'DELETE.' Together, these words indicate that the proofreader should either leave the text as it is or DELETE it, depending on the context.