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

Encyclopedia: Gigayear

• upper-middle-class
• Upper-Normandy
• uppercase
• uppercut
• uppermost
• uppish
• uppishly
• uppishness
• uppity
• uppityness
• UPPP
• Uppsala
• upraise
• upraised
• uprate
• uprear
• upright
• upright piano
• uprightly
• uprightness
• uprise
• uprising
• upriver
• uproar
• uproarious