Of somebody’s day Definition 1 of 3Pro Tip 1/3Historical Context Use it to reference someone's prime within their historical context or era. The author was a celebrated thinker of his day. Pro Tip 2/3Comparative Excellence Implies comparatively the best among peers during a past time period. She was the voice of her day, unrivaled in opera. Pro Tip 3/3Nostalgic Tone Often used with a nostalgic tone, looking back at someone's peak moments. He was the fastest sprinter of his day.