"Nonplussed" is an adjective that means to be perplexed or confused to the point of being unable to think or respond. From the clue provided, "at sea" is likely being used figuratively to mean in a state of uncertainty or confusion.
Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: Discombobulated. Explanations are generated by AI and may be inaccurate.