Why is the ninth month called September?
1630s, from Latin vividus "spirited, animated, lively," from vivus "alive," from PIE *gwei- (see vital). Extension to colors is first recorded 1660s. Sense of "strong, distinct" (as of memories, etc.) is from 1680s; that of "very active or intense" (as of imagination, interest, etc.) is from 1853. Related: Vividly; vividness.