The chief port of Russia's Pacific coast (11)
I believe the answer is:
vladivostok
'the chief port' is the definition.
The definition and answer can be both locations as well as being singular nouns.
Maybe you can see a link between them that I can't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for vladivostok that I've seen before include "Russian Pacific Ocean port" , "Seaport of Asian Russia" , "Asian city" , "Russian city, Trans-Siberian Railway terminus" .)