Herd heard in port (5)
I believe the answer is:
cowes
'port' is the definition.
Although both the answer and definition are verbs, they are not in the same form of the verb.
'herd heard' is the wordplay.
'herd' becomes 'cows'.
'heard' shows a homophone (sound like).
'cows' is a homophone of 'COWES'.
'in' is the link.
Can you help me to learn more?
(Other definitions for cowes that I've seen before include "where regatta happens" , "English town?" , "IOW regatta venue" , "IOW regatta town" , "Isle of Wight regatta town" .)