das Relikt
relic
An object, custom, or structure that has remained from an earlier time and serves as evidence of that era.
Die alte Stadtmauer ist ein Relikt aus dem Mittelalter.
The old city wall is a relic from the Middle Ages.

relic
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relic
An object, custom, or structure that has remained from an earlier time and serves as evidence of that era.
Die alte Stadtmauer ist ein Relikt aus dem Mittelalter.
The old city wall is a relic from the Middle Ages.

The context makes it clear which meaning is intended. If it is about history, architecture, or society, it is a remnant from an earlier time. If it is about religion, saints, or churches, it refers to a venerated object.
Die alte Fabrik ist ein Relikt der industriellen Revolution.
The old factory is a relic of the Industrial Revolution.
To name the era or origin of a relic, the preposition 'aus' (from) with the dative is almost always used.
Dieses Telefon mit Wählscheibe ist ein Relikt aus den 70er Jahren.
This rotary phone is a relic from the 1970s.
The word 'Relikt' (relic) is used mainly in written language and in educated or formal contexts such as museums, documentaries, or specialist articles.
Der Historiker bezeichnete die Monarchie als ein überholtes Relikt.
The historian described the monarchy as an outdated relic.
In a religious context, a relic is often 'aufbewahrt' (kept) in a treasury or shrine and 'verehrt' (venerated) by believers.
Tausende Pilger kamen, um das heilige Relikt zu verehren.
Thousands of pilgrims came to venerate the holy relic.
rest / remainder
'der Rest' and 'das Relikt' can both mean something that is left over from earlier or after a larger whole. 'der Rest' is neutral and very general. It can be a small part of almost anything, for example food, material, or money. 'das Relikt' means something that has been preserved from an earlier time and still shows that time. It often sounds historical or cultural. Learners may confuse the words because both describe something left over. But not every 'Rest' is a 'Relikt'. A 'Relikt' usually has a connection to the past.

Die alte Stadtmauer ist ein Relikt aus dem Mittelalter.
The old city wall is a relic from the Middle Ages.
Nach dem Umzug blieb nur ein kleiner Rest Farbe im Eimer.
After the move, only a small amount of paint was left in the bucket.