Retiring, but souvenir has been ordered (11)

I believe the answer is:

unobtrusive

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'retiring' is the definition.
(similar in meaning)

'but souvenir has been ordered' is the wordplay.
'but souvenir' can be anagrammed to 'UNOBTRUSIVE'.
Though, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for unobtrusive that I've seen before include "Shy" , "Modest" , "low-key" .)

I've seen this clue in The Daily Express.

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