Bí·o-Bí·o 
(bē′ō-bēō)
(bē′ō-bēō) A river of central Chile flowing about 385 km (240 mi) generally northwest from the Andes to the Pacific Ocean near Concepción.
- x-ray
- x-ray astronomy
- x-ray burster
- x-ray crystallography
- x-ray diffraction
- x-ray fish
- x-ray microscope
- x-ray photoemission spectroscopy
- x-ray spectrometer
- x-ray spectrometry
- x-ray spectroscope
- x-ray spectroscopy
- x-ray star
- x-ray therapy
- x-ray tube
- Xuthus
- Xuzhou
- xyl-
- xyl-
- xylan
- xylem
- xylene
- xylidine
- xylitol
- xylo-