Arecibo (ärəsēˈbō) [key], city (1990 pop. 93,385), N Puerto Rico, a port on the Atlantic Ocean at the mouth of the Rio Grande de Arecibo. It has rum distilleries and is the commercial and industrial center of a region that produces coffee, tobacco, sugarcane, and pineapples. The Arecibo Observatory, an important radio-astronomy facility, is nearby. Arecibo was founded in 1616.