s.s. ship definition
A ship prefix is a combination of letters, usually abbreviations, used in front of the name of a civilian or naval ship. Prefixes for civilian vessels may either identify the type of propulsion, such as PS for paddle steamer, or purpose, such as RV for research vessel. Civilian prefixes are often used inconsistently, and frequently not at all. Sometimes a slash is used to separate the letters, as in M/S.