Sailor from the East spies skinny partygoer (9)
I believe the answer is:
socialite
'partygoer' is the definition.
(I've seen this before)
'sailor from the east spies skinny' is the wordplay.
'sailor' becomes 'os' (ordinary seaman).
'from the east' says the letters should be written backwards (on a map from right to left).
'spies' becomes 'CIA' (Central Intelligence Agency).
'skinny' becomes 'lite' (I can't explain this - if you can you should give a lot more credence to this answer).
'os' in reverse letter order is 'so'.
'so'+'cia'+'lite'='SOCIALITE'
Can you help me to learn more?
(Other definitions for socialite that I've seen before include "One who frequents fashionable circles" , "Partygoer" , "Party-going celeb" , "One of the fashionable classes" .)