Notice, when the train moves out, looking very happy (7)

I believe the answer is:

radiant

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'happy' is the definition.
(thesaurus)

'notice when the train moves out' is the wordplay.
'notice when' becomes 'ad' (short for advert. I am not sure about the 'when' bit.).
'moves' indicates anagramming the letters.
'out' is an insertion indicator.
'train' with letters rearranged gives 'riant'.
'ad' placed into 'riant' is 'RADIANT'.

'looking very' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for radiant that I've seen before include "Shining; joyful" , "with good humour" , "Straight line" , "Splendid; heater type" , "Effulgent" .)

I've seen this clue in the Evening Standard.

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