Large port is charged (5)
I believe the answer is:
laden
'is charged' is the definition.
(I've seen this before)
'large port' is the wordplay.
'large' becomes 'l'.
'port' becomes 'aden' (I've seen this before**).
'l'+'aden'='LADEN'
(Other definitions for laden that I've seen before include "full cargo ship" , "Freighted" , "Carrying goods" , "cargo aboard" , "Carrying a load" .)