1. (cosmology) one billion (10^9) years
   "the universe is approximately 14 gigayears old"

Encyclopedia: Gigayear

• Adar Sheni
• adaxial
• adaxially
• add
• add on
• add to
• add together
• add up
• add-in
• addable
• addax
• Addax nasomaculatus
• addend
• addendum
• adder
• adder's fern
• adder's tongue
• adder's tongue fern
• addible
• addict
• addicted
• addiction
• addictive
• adding machine
• Addis Ababa