Unfocused as smile broke out (7)

I believe the answer is:

aimless

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'broke out' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I don't see?

'unfocused as smile' is the wordplay.
'as smile' can be anagrammed to 'AIMLESS'.
But, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for aimless that I've seen before include "Without objectives" , "Without purpose or plan" , "lacking direction" , "With no plan or programme" , "Drifting with no purpose" .)

I've seen this clue in The Mirror.

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