timeless

Short definition from Wiktionary

Adjective

1. 1
   Eternal.
2. 2
   Not affected by time; ageless.
3. 3
   Done at an improper time; unseasonable; untimely.
4. 4
   Not decreasing over time in quality and appeal.
5. 5
   Without a time limit; untimed.

Noun

1. 1
   A gene encoding an essential protein that regulates circadian rhythm, normally written in italics: timeless.