Initially only ask about a port (5)
I believe the answer is:
osaka
'port' is the definition.
(I know that Osaka is a port)
'initially only ask about a' is the wordplay.
'initially' says to take the initial letters.
'about' is an anagram indicator.
The first letter of 'only' is 'o'.
'ask' with letters rearranged gives 'sak'.
'o'+'sak'+'a'='OSAKA'
(Other definitions for osaka that I've seen before include "S. Japan port, bay" , "Place" , "Port city of southern Honshu" , "Major port and commercial and industrial centre on Honshu" , "Asian" .)