It's linked with a certain reaction (5)

I believe the answer is:

chain

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

'reaction' is the definition.
(chain reaction is a kind of reaction)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for chain that I've seen before include "Event series" , "Series of connected links" , "Shackle" , "group of shops here" , "Paper decoration" .)

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.