Large port, fully loaded (5)
I believe the answer is:
laden
'fully loaded' is the definition.
(I've seen this in another clue)
'large port' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'port' becomes 'aden' (port in Yemen).
'l'+'aden'='LADEN'
(Other definitions for laden that I've seen before include "Loaded with cargo or burden" , "cargo aboard" , "Burdened, loaded" , "Like cargo boat" , "Loaded - oppressed" .)