Less than 90º

I believe the answer is:

acute

(Other definitions for acute that I've seen before include "Grave" , "Extremely sharp or intense" , "Sharp; type of accent" , "quick on the uptake" , "Incisive" .)

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.