Party had endless port (4)
I believe the answer is:
doha
'port' is the definition.
(port in Qatar)
'party had endless' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'endless' means to remove the last letter.
'had' with its last letter taken away is 'ha'.
'do'+'ha'='DOHA'
(Other definitions for doha that I've seen before include "Gulf resort" , "Trade round" , "Capital of Qatar" .)