Solution: Relating to gaps - NYT Crossword

“Lacuna” is classic crosswordese; Latin for “lake,” and used to describe a blank spot or gap, often in a manuscript. LACUNAR was new to me, and so was SERTS at 47D, which is too bad, as Jose (or Josep) Maria Sert is responsible for the massive mural at 30 Rockefeller Plaza that depicts “American Progress.” Interesting story, which I also did not know: The Rockefellers originally commissioned Diego Rivera to decorate their imposing lobby, and Rivera did indeed do the work, but when it was discovered that he had included imagery of Lenin, the family had it destroyed and then hired Sert.