Slowly father enters Greek port (7)
I believe the answer is:
lepanto
'greek port' is the definition.
(I've seen this in another clue)
'slowly father enters' is the wordplay.
'slowly' becomes 'lento' (musical instruction).
'father' becomes 'pa' (pa can mean dad or father).
'enters' is an insertion indicator.
'lento' going around 'pa' is 'LEPANTO'.
(Other definitions for lepanto that I've seen before include "Polenta (anag.); battle" , "Famous 16th-century sea battle; on plate (anagram)" .)