Slackened and become loose in a rush (7)

I believe the answer is:

relaxed

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

'slackened' is the definition.
(I've seen this before)

'loose in a rush' is the wordplay.
'loose' becomes 'lax' (associated in meaning).
'in' is an insertion indicator.
'a rush' becomes 'reed' (I've seen this before).
'lax' put within 'reed' is 'RELAXED'.

'and become' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for relaxed that I've seen before include "composed" , "Having put one's feet up" , "Without tension" , "Made (a rule) less strict" , "Without strain or anxiety" .)

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.