Former openings for trade? (7)

I believe the answer is:

exports

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'former openings for trade?' is the definition.
I can't tell whether this defines the answer.

'former openings' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'openings' becomes 'ports' (port is a kind of opening).
'ex'+'ports'='EXPORTS'

Can you help me to learn more?

(Other definitions for exports that I've seen before include "foreign trade?" , "sends abroad" , "Goods or services sold abroad" , "goods going abroad" , "Foreign currency earners" .)

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

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