trocken
dry
Free of water or another liquid; not wet or damp.
Nach dem Regen war die Straße schnell wieder trocken.
After the rain, the street was quickly dry again.

dry
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dry
Free of water or another liquid; not wet or damp.
Nach dem Regen war die Straße schnell wieder trocken.
After the rain, the street was quickly dry again.

The adjective 'trocken' (dry) belongs to a word family with the verb 'trocknen' (to dry; to make something dry) and the noun 'die Trockenheit' (dryness; a state without water).
Die Wäsche trocknet in der Sonne sehr schnell.
The laundry dries very quickly in the sun.
The idiom 'im Trockenen sein' or 'im Trockenen sitzen' means to be protected from the rain. It can also be used metaphorically to mean 'to be safe'.
Zum Glück haben wir es noch vor dem Gewitter ins Haus geschafft und sitzen jetzt im Trockenen.
Luckily, we made it into the house before the thunderstorm and are now sitting in the dry.
The meaning 'nicht süß' (not sweet) is used almost exclusively for alcoholic drinks, especially wine and sparkling wine. The opposite is 'süß' (sweet) or 'lieblich' (medium-sweet).
Ich bevorzuge trockenen Rotwein zu einem kräftigen Essen.
I prefer dry red wine with a hearty meal.
In combination with words like 'Humor' (humor), 'Witz' (joke), or 'Bemerkung' (remark), 'trocken' (dry) describes a matter-of-fact, ironic, and not very emotional style.
Mit einer trockenen Bemerkung brachte er alle zum Nachdenken.
With a dry remark, he made everyone think.
When a topic, book, theory, or lecture is described as 'trocken' (dry), it means the content is very theoretical, abstract, and boring.
Der Professor hat es geschafft, das trockene Thema lebendig zu erklären.
The professor managed to explain the dry topic in a lively way.
In the context of alcoholism, 'trocken' (sober/dry) is a fixed term. A 'trockener Alkoholiker' (sober alcoholic) is a person who no longer drinks alcohol.
Seit er trocken ist, hat sich sein Leben komplett verändert.
Since he got sober, his life has completely changed.
In medicine, 'trocken' (dry) describes a cough without mucus production. People say 'trockener Husten' (dry cough) or 'trockener Reizhusten' (dry, irritating cough).
Gegen trockenen Husten hilft oft, viel Tee zu trinken.
Drinking a lot of tea often helps with a dry cough.
boring
'langweilig' and 'trocken' can both describe something as not very interesting. 'langweilig' is the general word: a film, an evening, or a lecture can be 'langweilig' if you feel bored by it. 'trocken' is more suitable for topics, texts, or lectures that are very factual, theoretical, and lack vivid examples. So a dry topic is often boring, but not everything boring is dry. 'trocken' especially describes the way something is presented.

Der Vortrag war sehr trocken, weil es keine Bilder und keine Beispiele gab.
The lecture was very dry because there were no pictures and no examples.
Der Film ist so langweilig, dass Paul fast eingeschlafen ist.
The film is so boring that Paul almost fell asleep.