Attributive Designating a programming problem affecting some computers, arising from the inability of software and firmware to process correctly dates of 1 January 2000 and later, owing to the numerical representation of calendar years by the last two digits only (predicted at the time to cause widespread disruption to computer systems); of or relating to this problem. Compare "Y2K", "millennium bug".
1990s; earliest use found in InformationWeek. From year + two + thousand [adjective]. Usually written with numerical symbol for the second element.