Smooth tranquillity once interrupting weather (6)

I believe the answer is:

sleeky

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

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

I cannot understand how the rest of the clue works.

Can you help me to learn more?

I've seen this clue in The Times and The Sunday 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.