das Gedächtnis
memory
The mental ability to store information, impressions, and experiences and recall them later.
Im Alter lässt das Gedächtnis oft nach.
In old age, memory often declines.

memory
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memory
The mental ability to store information, impressions, and experiences and recall them later.
Im Alter lässt das Gedächtnis oft nach.
In old age, memory often declines.

The word 'Gedächtnis' (memory) is related to the verb 'denken' (to think). The prefix 'Ge-' and the ending '-nis' together form an abstract concept that describes the result or place of thinking: memory.
Er hat viele alte Geschichten in seinem Gedächtnis bewahrt.
He preserved many old stories in his memory.
To describe the ability to remember, 'Gedächtnis' (memory) is often combined with the verb 'haben' (to have) and an adjective. Very common phrases are 'ein gutes Gedächtnis haben' (to have a good memory) or 'ein schlechtes Gedächtnis haben' (to have a bad memory).
Meine Großmutter ist 90 Jahre alt, aber sie hat immer noch ein ausgezeichnetes Gedächtnis.
My grandmother is 90 years old, but she still has an excellent memory.
When 'Gedächtnis' (memory) means the memory of a specific thing or person, it is almost always used with the preposition 'an' and the accusative case.
Das Gedächtnis an seine Kindheit machte ihn glücklich.
The memory of his childhood made him happy.
The phrase 'zum Gedächtnis an' (in memory of) is a fixed expression. It is used almost exclusively in the context of commemorating deceased people or historical events, often on monuments or at memorial services.
Die Familie stiftete eine Bank zum Gedächtnis an ihre verstorbene Mutter.
The family donated a bench in memory of their deceased mother.
memory / reminder
'die Erinnerung' and 'das Gedächtnis' are both connected to storing things from the past in the mind. An 'Erinnerung' is usually something individual: an image, a feeling, or a piece of information from an earlier time. 'Gedächtnis' refers more to the ability to store such things and recall them again. They can be confused because both are used to talk about the past. As a simple guide: many 'Erinnerungen' are stored in the 'Gedächtnis'.

Mein Großvater hat ein gutes Gedächtnis und kennt noch viele alte Geschichten.
My grandfather has a good memory and still knows many old stories.
Die Erinnerung an den ersten Schultag ist für Anna noch sehr lebendig.
The memory of her first day of school is still very vivid for Anna.