The term PART OF QED is composed of two crossword solutions, ERAT and QUOD. ERAT is a Latin verb meaning 'to have been' or 'to have existed, ' while QUOD is a Latin conjunction meaning 'BECAUSE' or 'for which.' Together, they form the phrase 'erat quod, ' which translates to 'it was BECAUSE' or 'it was for which, ' and is part of the Latin phrase 'QED, ' which stands for 'quod erat demonstrandum' and means 'which was to be demonstrated.'