"Wait . . . what?" (3)

I think it could be either:

Which length description are you looking for?:

whoa

(Other definitions for whoa that I've seen before include "horsy expression?" , "Instruction to a horse to stop" , "Command to horse to stop or stand still" , "Command for horse to slow or stop" , "Opposite of "Giddy-up!"" .)

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.