a professional clown employed to entertain a king or nobleman in the middle ages
In the courts of kings and queens in medieval Europe, the jester was the person whose job was to do silly things in order to make people laugh. = fool
n An officer formerly attached to a king's household, whose business it was to amuse the court by ludicrous actions and utterances, the absurdity being attested by his motley costume The king himself being attired with dignity, it took the world some centuries to discover that his own conduct and decrees were sufficiently ridiculous for the amusement not only of his court but of all mankind The jester was commonly called a fool, but the poets and romancers have ever delighted to represent him as a singularly wise and witty person In the circus of to-day the melancholy ghost of the court fool effects the dejection of humbler audiences with the same jests wherewith in life he gloomed the marble hall, panged the patrician sense of humor and tapped the tank of royal tears
{i} prankster, joker, one who makes jokes; one who works as a clown or entertainer (especially at a medieval court)