Trade through former harbours (7)
I believe the answer is:
exports
'trade through former harbours' is the definition.
The answer and definition can be both to do with ownership as well as being verbs in their -s form.
Maybe they are linked in a way I don't understand?
'former harbours' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'harbours' becomes 'ports' (I've seen this before).
'ex'+'ports'='EXPORTS'
Can you help me to learn more?
(Other definitions for exports that I've seen before include "goods going abroad" , "Foreign currency earners" , "Imports & - -" , "Goods or services sold abroad" , "foreign trade?" .)