Gua·dia·na 
(gwä-dyänə, -thyänä)
(gwä-dyänə, -thyänä) A river rising in south-central Spain and flowing about 780 km (485 mi) west and south partly along the Spanish-Portuguese border to the Gulf of Cádiz.
- photochemically
- photochemical smog
- photochemistry
- photochromatic
- photochromism
- photocoagulate
- photocoagulation
- photocompose
- photocomposition
- photoconduction
- photoconductive
- photoconductivity
- photocopier
- photocopy
- photocurrent
- photodecomposition
- photodegradable
- photodiode
- photodisintegration
- photoduplicate
- photoduplication
- photodynamic
- photodynamically
- photodynamics
- photodynamic therapy