See ship alongside port, for example, loaded with first of trunks (7)
I believe the answer is:
witness
'see' is the definition.
(I know that see can be written as witness)
'ship alongside port for example loaded with first of trunks' is the wordplay.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'alongside' is a charade indicator (letters next to each other).
'port for example' becomes 'wine' (port is a kind of wine).
'loaded with' means one lot of letters goes inside another.
'first of trunks' becomes 't' (1st letter of 'trunks').
'wine' going around 't' is 'witne'.
'ss' after 'witne' is 'WITNESS'.
(Other definitions for witness that I've seen before include "One who saw an event, may give evidence" , "One giving evidence" , "Court testifier" , "Evidence, proof" , "One sees and reports" .)