Heather takes in a Chinese ounce (5)

I believe the answer is:

liang

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'chinese ounce' is the definition.
The definition suggests a singular noun which matches the answer.

'heather takes in a' is the wordplay.
'heather' becomes 'ling' (synonyms).
'takes in' means one lot of letters goes inside another.
'ling' placed around 'a' is 'LIANG'.

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I've seen this clue in the Sydney Morning Herald.

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