Return strange material for jewellery (8)

I believe the answer is:

electrum

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'material for jewellery' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'return strange' is the wordplay.
'return' becomes 'elect' (I've seen this before).
'strange' becomes 'rum' (similar in meaning).
'elect'+'rum'='ELECTRUM'

Can you help me to learn more?

I've seen this clue in The Times.

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