Ouidah (wē´dä) or Whydah (hwī´də), town (1992 pop. 32,474), S Benin, a port on the Gulf of Guinea. It was the capital of a small state founded about the 16th cent. From the early 17th cent., Portuguese, French, and Dutch traders were intermittently active at Ouidah, whose name was derived by Europeans from a nearby Portuguese fort called São João Baptista de Ajudá (St. John of Adjuda). In the 18th and early 19th cent. Ouidah was an important export point for slaves. In the 1840s the French established a substantial trade with Ouidah, exchanging textiles, guns, and gunpowder for palm oil and ivory. The town was annexed by France in 1886. Ouiday is a center of the Vodoun (voodoo) religion.