With the shutter, it's less airy (6)

I believe the answer is:

closer

I'm a little stuck... Click here to teach me more about this clue!

'with' is the definition.
Both the answer and definition are adverbs. Perhaps they are linked in a way I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for closer that I've seen before include "One winds up" , "Less distant" , "Nearer as to time or event" , "Nearer in time or space" , "Cresol (anag.)" .)

I've seen this clue in the Evening Standard.

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.