Tranquil, laugh only about getting caught (7)

I believe the answer is:

halcyon

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

'tranquil' is the definition.
(I've seen this in another clue)

'laugh only about getting caught' is the wordplay.
'laugh' becomes 'ha'.
'only' becomes 'lyon' (I can't justify this - if you can you should believe this answer much more).
'about' becomes 'c' (abbreviation for circa).
'getting caught' means one lot of letters goes inside another.
'lyon' enclosing 'c' is 'lcyon'.
'ha'+'lcyon'='HALCYON'

Can you help me to learn more?

(Other definitions for halcyon that I've seen before include "Balmy" , "Poetic name for kingfisher" , "Calm and happy - kingfisher" , "Happy and carefree" , "Tropical kingfisher" .)

I've seen this clue in The Daily Express.

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.