
abdrehen
to turn off
To interrupt the supply of something (e.g., water, gas, electricity) by turning something.
Kannst du bitte das Wasser abdrehen, während ich die Dichtung wechsle?
Can you please turn off the water while I change the seal?
to turn off / to freak out
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to turn off
To interrupt the supply of something (e.g., water, gas, electricity) by turning something.
Kannst du bitte das Wasser abdrehen, während ich die Dichtung wechsle?
Can you please turn off the water while I change the seal?

to freak out
Colloquial for losing control, going crazy, or reacting extremely angrily.
Als er merkte, dass sein Auto abgeschleppt wurde, ist er völlig abgedreht.
When he realized that his car was being towed, he completely freaked out.

to turn away
To change direction, to turn off. Often used for ships or airplanes.
Kurz vor der Küste musste das Schiff wegen des Sturms nach Westen abdrehen.
Shortly before reaching the coast, the ship had to turn west because of the storm.

to finish filming
To finish filming a movie or a scene.
Die letzte Szene des Films wurde gestern Abend abgedreht.
The final scene of the film was finished yesterday evening.
'Abdrehen' is a separable verb. In a main clause, the prefix 'ab-' goes at the end; in subordinate clauses and in the infinitive, it remains attached to the verb.
Bitte dreh die Heizung ab, es ist zu warm.
Please turn off the heating; it's too warm.
You can recognize the meaning of 'abdrehen' from the context. If it is about devices or pipes/lines (water, gas), the technical meaning is intended. In connection with ships or airplanes, it refers to a change of direction. When talking about people, the colloquial meaning 'verrückt werden' (to go crazy) is often meant.
Der Pilot musste wegen des Gewitters sofort abdrehen.
The pilot had to turn away immediately because of the thunderstorm.
In the technical meaning, 'abdrehen' is often combined with things whose supply can be stopped. Typical phrases are: 'das Wasser abdrehen' (to turn off the water), 'den Hahn abdrehen' (to turn off the tap), 'das Gas abdrehen' (to turn off the gas), or 'die Heizung abdrehen' (to turn off the heating).
Bevor du in den Urlaub fährst, solltest du den Haupthahn für das Wasser abdrehen.
Before you go on vacation, you should turn off the main water tap.
The meaning 'verrückt werden' (to go crazy) is strongly colloquial. Since it describes a sudden change of state, the perfect tense is formed with 'sein' (to be).
Die Fans sind nach dem Siegestor völlig abgedreht.
The fans completely freaked out after the winning goal.
to turn / contact
Wenden and abdrehen can both describe a change of course. A ship wendet when it turns around and then travels in the opposite direction. It dreht ab when it leaves its previous course without necessarily turning around completely.

Das Schiff dreht nach Westen ab und folgt einem neuen Kurs.
The ship turns west and follows a new course.
Das Schiff wendet und fährt zum Hafen zurück.
The ship turns around and heads back to the harbor.