Rumour about harbour (6)
I believe the answer is:
report
'rumour' is the definition.
(I've seen this before)
'about harbour' is the wordplay.
'about' becomes 're' (regarding).
'harbour' becomes 'port' (I've seen this before).
're'+'port'='REPORT'
(Other definitions for report that I've seen before include "Give an account" , "Sharp sound of a gun firing" , "Spoken/written account" , "Journalist's account - explosive noise" , "Porter (anag.)" .)