das Jahrtausend
millennium
A period of one thousand years.
Die Erfindung des Buchdrucks war ein Meilenstein im zweiten Jahrtausend.
The invention of the printing press was a milestone in the second millennium.

millennium
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millennium
A period of one thousand years.
Die Erfindung des Buchdrucks war ein Meilenstein im zweiten Jahrtausend.
The invention of the printing press was a milestone in the second millennium.

The word is a clear compound of 'das Jahr' (year) and 'tausend' (thousand). So it literally refers to a period of one thousand years.
Die alten Pyramiden sind mehrere Jahrtausende alt.
The ancient pyramids are several millennia old.
'Jahrtausend' (millennium) follows a clear pattern for naming periods of time, which is also used in 'das Jahrzehnt' (decade, 10 years) and 'das Jahrhundert' (century, 100 years). This helps you learn the words as a system.
Innerhalb eines Jahrzehnts hat sich die Technologie rasant entwickelt.
Within a decade, technology developed rapidly.
To name a specific millennium, you use an ordinal number. A very well-known fixed expression is 'die Jahrtausendwende' (the turn of the millennium) for the transition into the year 2000.
Viele wichtige philosophische Ideen entstanden im ersten Jahrtausend vor Christus.
Many important philosophical ideas emerged in the first millennium BC.
The exaggerated, colloquial meaning is often recognizable from the context of personal impatience. Sometimes it is intensified by words like 'gefühlt' (felt, as in 'it felt like') to emphasize the subjective perception.
Ich warte schon ein gefühltes Jahrtausend auf eine Antwort von der Behörde.
I've been waiting what feels like a millennium for an answer from the authorities.
century
'das Jahrhundert' and 'das Jahrtausend' both refer to long periods of time. The important difference is the length: a century has one hundred years, while a millennium has one thousand years. They are easy to confuse because both begin with 'Jahr-' and often appear in history or culture. For events like 'das 20. Jahrhundert' (the 20th century), 'Jahrhundert' fits. For very large historical periods, 'Jahrtausend' fits. Colloquially, 'Jahrtausend' can also mean 'a very long time' in an exaggerated way.

Diese alte Stadt wurde schon vor mehr als einem Jahrtausend gegründet.
This old city was founded more than a millennium ago.
Im letzten Jahrhundert hat sich das Leben in vielen Städten stark verändert.
In the last century, life in many cities changed a lot.