A sailor is either someone who sails boats of some kind for a living, or someone who is below the level of an officer in the Navy.
A scientist is someone who works to gain more knowledge about the sciences, particularly natural and physical sciences. Scientists work using scientific method as they learn.
A secretary is someone who handles a lot of paperwork in an office. They will take notes at meetings, take dictations, type up letters and file papers.
A seer is a person who can see the future, or who has profound insight or knowledge. A similar word to seer is prophet.
A sentry is someone who stands guard over something, to protect it. The sentry in this picture is guarding the entry to the Tower of London, which contains the Queen's jewels.
A shearer is someone who clips the wool, called a fleece, from sheep or other wooly animals.
A skater is someone who skates, either on ice skates, roller skates or on a skateboard. People might skate just for fun, or professionally for money.
Skipper is an informal word meaning the captain of a ship, or simply the person who is in control of the ship.
A sniper is someone who can shoot a target from a very long distance away, from a concealed position.