Longest-serving U.S. first lady, informally

I believe the answer is:

eleanor

(Other definitions for eleanor that I've seen before include "Near Leo (anag) - girl's name" , "- - Rigby: Beatles song" , "Franklin D. Roosevelt's wife" , "- of Aquitaine, - of Castile (queens)" , "Wife of F. D. Roosevelt" .)

I've seen this clue in The New York Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.