Nancy ____ was the USA's first lady, 1981-1989 (6)
I believe the answer is:
reagan
(Other definitions for reagan that I've seen before include "US president nineteen eighty one to ninteen eighty nine" , "40th US president, Ronald" , "Former US president" , "40th president of the United States" , "Ronald . . . . . ., 40th president of USA" .)