adressieren
to address
To write or print the recipient's address on a letter, package, or other item being sent.
Bitte adressieren Sie den Umschlag an die Personalabteilung.
Please address the envelope to the HR department.

to address
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to address
To write or print the recipient's address on a letter, package, or other item being sent.
Bitte adressieren Sie den Umschlag an die Personalabteilung.
Please address the envelope to the HR department.

The verb 'adressieren' (to address) is derived directly from the noun 'die Adresse' (address). The ending '-ieren' is often used to form verbs from nouns, often loanwords.
Vergiss nicht, den Brief zu adressieren, bevor du ihn einwirfst.
Don't forget to address the letter before you mail it.
When you name the recipient, the preposition 'an' with the accusative is used. This applies both to postal items and to words or criticism.
Der Brief ist an die falsche Abteilung adressiert.
The letter is addressed to the wrong department.
The object of the verb reveals the meaning. If it is a physical object like 'Brief' (letter) or 'Paket' (package), the literal meaning is meant. If it is something abstract like 'Problem' (problem), 'Frage' (question), or 'Kritik' (criticism), the figurative meaning is meant.
Ich muss noch das Paket adressieren.
I still have to address the package.
In the meaning 'to bring up a topic', 'adressieren' (to address) is rather formal. You often find it in politics, in the news, in business, or in academic discussions.
Die Studie adressiert ein wichtiges gesellschaftliches Problem.
The study addresses an important social problem.
to treat / to deal with
'behandeln' and 'adressieren' can both mean that you deal with a topic or problem. 'behandeln' is more general and more natural when a text, conversation, or lesson explains or discusses a topic in detail. 'adressieren' sounds more formal and often means that you address a problem directly or direct something to a person or group. Learners may confuse the words because both can fit with topics and problems. As a simple guide: a book 'behandelt' a topic; an email 'adressiert' a problem or is directed at specific people.

Die Chefin adressiert die Beschwerden der Kunden direkt im Meeting.
The boss addresses the customers' complaints directly in the meeting.
Im Kurs behandeln wir heute das Thema Bewerbung.
In the course, we are dealing with the topic of job applications today.