Stuff stored in empty glass units (5)

I believe the answer is:

grams

'units' is the definition.
(gram is a kind of unit)

'stuff stored in empty glass' is the wordplay.
'stuff' becomes 'ram' (ram can mean to stuff or push).
'stored in' means one lot of letters goes inside another.
'empty' means to remove the middle letters.
'glass' with its centre removed is 'gs'.
'ram' placed within 'gs' is 'GRAMS'.

(Another definition for grams that I've seen is " Metric unit of mass".)

I've seen this clue in The Independent.

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