'astarboard' originates from the combination of the prefix 'a-' (on, in, to) and the word 'starboard' (the right side of a ship).

'astarboard' appears in Middle English as a compound of 'a-' + Old English 'steorbord' (steer-side); over time it was used in nautical English alongside forms like 'to starboard' and eventually became less common.

Initially it meant 'on or toward the steering side (right) of a ship'; the core meaning has been largely preserved, though the form is now archaic or literary compared with the more common phrase 'to starboard'.