Meaning

adjective relating to a millennium or span of a thousand years

originThe adjective is a learned borrowing from Late Latin mīllennium (“millennium”) + English -al (suffix meaning ‘of or pertaining to’ forming adjectives; and forming nouns). The English word may be analysed as millennium + -al or milli- (prefix meaning ‘thousand’) + -ennial (suffix meaning ‘years’). Adjective sense 5 (“of or relating to, or characteristic of, people born in the last two decades of…

Etymology from Wiktionary, CC BY-SA 3.0