Not used as an ordinary word in modern Chinese; it lingers mainly in given names and as an old variant of 畅 (smooth; free-flowing). It joins 永 (long-lasting) and 日 (day) to picture a long daylight.
register
Archaic and literary; today seen almost only as a name character, not in speech.
The sun radical tucked at the upper right. It supplies the daylight idea, so 永 plus 日 reads as a long day, grouping the character with time words like 明 and 时.
Wraps the lower left and means lasting or drawn-out. Paired with the sun it gives the idea of a long-stretching day, the same "endless" sense seen in 泳 and 咏.
