the.com/time capsule

means A container of objects and messages deliberately sealed away to be opened by people at a specified future date.

from A 20th-century compound — simply 'time' plus 'capsule,' the latter from Latin capsula, a 'small box' (diminutive of capsa, 'case'). The word capsule had already drifted into meaning any small sealed container, so pairing it with 'time' was a fairly literal, logical coinage rather than a word with deep ancient roots. The practice itself got a famous publicity boost from the 1939 New York World's Fair, which buried a container of artifacts explicitly dubbed a 'time capsule' and meant to be opened 5,000 years later — an event that helped fix both the term and the ritual in popular imagination.