The word "erst" means "previously" or "formerly." It is an adverb that typically refers to a past time or previous state of something. In the context of the clue "Once, once," it suggests that something occurred or existed in the past.
Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: Formerly, in the past. Explanations are generated by AI and may be inaccurate.