Sixtieth/ˈsɪkstiəθ/ Definition 1 of 2Pro Tip 1/3Milestone Moments Used to mark significant events or ages, especially ones that celebrate decades. Grandma's sixtieth birthday was unforgettable. Pro Tip 2/3Historical Context Use 'sixtieth' to reference anniversaries of historical or notable events. The nation celebrated the sixtieth anniversary of the moon landing. Pro Tip 3/3Academic Achievement Often used in education to signify a particular place among graduates or rankings. She graduated sixtieth in her class.