QUOD' (4 letters) QED Word is a term used in mathematics and logic to signify the end of a proof. It is an abbreviation for the Latin phrase 'Quod Erat Demonstrandum', which translates to 'That Which Was To Be Demonstrated'. The two crossword solutions, ERAT and QUOD, are both Latin words that are part of the phrase. ERAT means 'was' and QUOD means 'that which'. Together, they form the phrase 'That Which Was To Be Demonstrated'.