lifeday means A day of someone's life; chiefly in plural: a lifetime. Lexicurio rates it Sui generis — a strength score of 89 out of 100.
noun
- A day of someone's life; chiefly in plural: a lifetime.“For loth in his lifdayes · for likyng of drynke / Dede bi his douȝtres · þat þe deuel lyked.”