On a ship, what is the opposite of the starboard?

Port is the side opposite of starboard

'Port' and 'left' both have 4 letters - an easy way to remember which side is which.

larboard

Well, since you mention "larboard" I'll give the full story.

Since about 1300 the right side was "steorboard" meaning "steered side" as Germanic ships tended to be steered by paddles on the right side. The left side was "ladde-board" literally meant laden-side, the side on which the ship was loaded. By comparison with starboard this came to be pronounced larboard in the 16th century. Also in the 16th century, the left of ships was also informally called the port side. Due to the possibilty of confusion over the similarity of starboard and larboard, port became the standard term for the left by Admiralty order in 1844 and in the US Navy in 1846.

Another memory cue is "there's no red port left in the bottle", port side lights being red and on the left of the vessel. Starboard is green and right.
Interesting explanation gmack, we learn something every day!

Thanks Picq. At our school carol services, people with red tickets sat on the left of the chapel and those with green tickets sat on the right. As our Orcadian chaplain used to point out, the reason was nautical.

I presume the reason why port at a meal is traditionally passed to the left is also nautical.