
abrupt
Happening suddenly, unexpectedly, and without warning or transition.
Das Gespräch fand ein abruptes Ende, als das Telefon klingelte.
The conversation came to an abrupt end when the phone rang.
Loading your saved state.

Happening suddenly, unexpectedly, and without warning or transition.
Das Gespräch fand ein abruptes Ende, als das Telefon klingelte.
The conversation came to an abrupt end when the phone rang.

In behavior or communication, brief, brusque, and seeming unfriendly.
Seine abrupte Antwort auf meine Frage hat mich etwas vor den Kopf gestoßen.
His abrupt answer to my question threw me off a bit.

steep
Referring to terrain or a landscape: dropping very steeply.
Die Küste fällt hier abrupt ins Meer ab.
The coast drops steeply into the sea here.
Although 'abrupt' is an adjective, it is very often used like an adverb to describe a verb. It answers the question 'How does something happen?' and then means 'suddenly and unexpectedly.'
Der Fahrer bremste abrupt, um einen Unfall zu vermeiden.
The driver braked abruptly to avoid an accident.
You can recognize the exact meaning of 'abrupt' from the context. If it refers to an action or event, it means 'suddenly.' If it refers to communication, it means 'brusque.' In connection with landscapes, it means 'steep.'
Die Musik hörte abrupt auf.
The music stopped abruptly.
In the meaning of 'plötzlich' (suddenly), 'abrupt' is often used with verbs that describe an end or interruption. Typical combinations are 'abrupt enden' (to end abruptly), 'abrupt stoppen' (to stop abruptly), or 'abrupt abbrechen' (to break off abruptly).
Die Verhandlungen wurden abrupt abgebrochen.
The negotiations were broken off abruptly.
When 'abrupt' describes a person's behavior, it has a negative, unfriendly connotation. An 'abrupte Antwort' (abrupt answer) is not only short, but is also perceived as rude or brusque.
Ihre abrupte Reaktion zeigte allen, dass sie verärgert war.
Her abrupt reaction showed everyone that she was annoyed.
suddenly
Both words can describe an unexpected, rapid change or ending. „Plötzlich“ mainly emphasizes the surprising timing, while „abrupt“ also shows that the transition was harsh and happened without any intermediate stage. Use „abrupt“ when the lack of a transition is noticeable, and „plötzlich“ for a general sense of surprise.

Das Gespräch endete abrupt, ohne dass jemand sich verabschiedete.
The conversation ended abruptly, without anyone saying goodbye.
Das Gespräch endete plötzlich, weil jemand an der Tür klingelte.
The conversation suddenly ended because someone rang the doorbell.