Erat is the third-person singular imperfect of the Latin verb "esse," which means "to be." In the context of "Part of Q.E.D.," it refers to the mathematical proof's final step, indicating that what was to be demonstrated has been proven.
Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: Part of Q.E.D.. Explanations are generated by AI and may be inaccurate.