Answer: PLEDGE

Pledge can have multiple meanings depending on the context. In the given clue "Sister-to-be, say," it suggests that the word "pledge" refers to someone who is about to become a sister, possibly in a religious or sorority context. A pledge is a person who is in the early stages of joining or committing to a group or organization, often by making a promise or commitment.

Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: Sister-to-be, say. Explanations are generated by AI and may be inaccurate.