Meaning

noun the left side of a ship or aircraft to someone who is aboard and facing the bow or nose

adjective located on the left side of a ship or aircraft

originFrom Middle English ladde-bord, latebord, most likely referring to the side of the ship on which cargo was loaded. Changed to larboard in the 1500s by association with starboard. (Texts from the 1500s have spellings like lerbord, leereboord, larboord, corresponding to how they spell sterbord, steereboord, starboord.)

Etymology from Wiktionary, CC BY-SA 3.0