authentisch
authentic
Real, original, and not fake or imitated.
Dies ist eine authentische Unterschrift des Autors.
This is an authentic signature of the author.

authentic
Loading your saved state.
authentic
Real, original, and not fake or imitated.
Dies ist eine authentische Unterschrift des Autors.
This is an authentic signature of the author.

The meaning of 'authentisch' (authentic) depends on the noun. If it refers to an object, it means 'real' or 'original'. If it refers to a person or their behavior, it means 'credible' or 'true to oneself'.
Das Museum stellt ein authentisches Manuskript aus dem Mittelalter aus.
The museum is exhibiting an authentic manuscript from the Middle Ages.
In the meaning of 'real', 'authentisch' (authentic) is often used for things whose origin or originality is important. Typical examples are: an authentic document, an authentic signature, an authentic recipe, or an authentic atmosphere.
In diesem Restaurant kann man authentische italienische Küche genießen.
In this restaurant, you can enjoy authentic Italian cuisine.
When a person is described as 'authentisch' (authentic), this is usually seen positively. Typical verbs in this context are 'authentisch wirken' (to come across as authentic), 'authentisch sein' (to be authentic), and 'authentisch bleiben' (to remain authentic).
Es ist ihm wichtig, auch im Beruf authentisch zu bleiben.
It is important to him to remain authentic at work as well.
natural / of course
'natürlich' and 'authentisch' can both describe a person or their behavior as seeming genuine. 'natürlich' emphasizes that someone acts in a relaxed, unaffected way and not artificially. 'authentisch' goes a little further: the person seems credible and stays true to themselves. 'natürlich' works well for spontaneous behavior or a pleasant manner. 'authentisch' is more often used when evaluating the overall impression of a person, a speech, or a performance.

Der Handwerker wirkt authentisch, weil er offen über seine Fehler spricht.
The craftsman comes across as authentic because he speaks openly about his mistakes.
Vor der Kamera wirkt sie ganz natürlich und lacht viel.
In front of the camera, she seems completely natural and laughs a lot.