Just shattered by some emergency (4)

I believe the answer is:

mere

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'just' is the definition.
('just' can mean 'mere' or 'only')

'shattered by some emergency' is the wordplay.
'shattered by' becomes 'mer' (I can't justify this - if you can you should believe this answer much more).
'some' suggests taking the first letters.
The first letter of 'emergency' is 'e'.
'mer'+'e'='MERE'

Can you help me to learn more?

(Other definitions for mere that I've seen before include "Nothing more than - water" , "Pure; lake" , "Lake (and nothing else?)" , "of no significance" , "Pool, small lake" .)

I've seen this clue in the Evening Standard.

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