Spanish Main
Spanish colonies in the Americas, stretching from Panama to the Orinoco River and including the Carribean sea.

Splice the mainbrace
To have a drink. Or, perhaps, several drinks.

Spyglass
A telescope.

Starboard
The right side of the ship when you are facing toward her prow.

Strait
A narrow stretch of water between areas of land.
  Sutler
A merchant in port, selling the various things that a ship needed for supplies and repairs.

Swab
A disrespectful term for a seaman. "Man that gun, ye cowardly swabs!"

Walk the plank
A piratical execution. The victim, usually blindfolded or with bound hands or both, is forced to walk along a plank laid over the ship's side, to fall into the water below. Except this seems to be a total invention; it first appeared in 19th-century fiction, long after the great days of piracy.
 
         
 
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