Serene, unruffled (6)

I believe the answer is:

placid

I believe this is a double definition.

'serene' is the first definition.
(synonyms)

'unruffled' is the second definition.
(synonyms)

(Other definitions for placid that I've seen before include "Calm, unruffled" , "Cool and unruffled" , "Calm, peaceful" , "Calm and not easily upset" , "Quiet and still" .)

I've seen this clue in The Guardian.

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.