A soothsayer is someone who can foretell the future. If the convincing soothsayer at the state fair tells you you'll soon meet someone tall, dark, and handsome, you'll probably keep your eye out for someone who fits that description.
A fortune teller is also known as a soothsayer, or someone who claims to be able to predict the future. Long ago, a soothsayer might have been considered a useful consultant, even for a government, but today soothsayers are more likely to be scoffed at. Still, there are many soothsayers who have successful businesses telling people's fortunes and giving advice. Soothsayer comes from the Old English word for "truth," combined with "say," together meaning "an act of speaking the truth."