Cut off some of the beams? (6)

I believe the answer is:

darken

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

'cut' is the definition.
The definition and answer can be both related to change as well as being verbs in their base form.
Perhaps you can see an association between them that I can't see?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for darken that I've seen before include "Make less light" , "Dim" , "Cast a shadow over" , "Cloud over" , "Grow blacker" .)

I've seen this clue in The Globe and Mail.

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.