Mature crowd retreats without casualties (7)

I believe the answer is:

blossom

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

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

I don't understand how the remainder of the clue works.

(Other definitions for blossom that I've seen before include "Grow" , "Yield flowers" , "Flowers (on tree, shrub)" , "Come into flower" , "Fruit tree flowers" .)

I've seen this clue in The Sun and The Guardian.

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