Sailor reportedly rowed alongside (6)
I believe the answer is:
aboard
'alongside' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for aboard that I've seen before include "on deck" , "On (a ship/plane)" , "in a car" , "ready to take off" , "'On a ship or train, say (6)'" .)