schwach
weak
Having little physical strength or energy; the opposite of strong.
Nach der Grippe fühlte sie sich noch wochenlang schwach.
After the flu, she still felt weak for weeks.

weak
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weak
Having little physical strength or energy; the opposite of strong.
Nach der Grippe fühlte sie sich noch wochenlang schwach.
After the flu, she still felt weak for weeks.

'Schwach' (weak) belongs to a word family. The noun is 'die Schwäche' (weakness), and the verb is 'schwächen' (to weaken). All three words refer to the concept of low strength or intensity.
Jeder Mensch hat Stärken und Schwächen.
Every person has strengths and weaknesses.
The expression 'schwach werden' (to give in) means not being able to resist a temptation. It describes the moment of decision when you give in.
Bei Schokolade werde ich immer schwach.
I always give in when it comes to chocolate.
To express that you are not good at a particular subject or skill, you use the fixed structure 'schwach in' (weak in) + dative. Typical examples are school subjects or sports.
Mein Sohn ist schwach in Mathematik, aber gut in Sprachen.
My son is weak in mathematics, but good at languages.
The noun that 'schwach' (weak) describes reveals the exact meaning. A 'schwacher Kaffee' (weak coffee) has little aroma, a 'schwaches Argument' (weak argument) is not convincing, and a 'schwaches Herz' (weak heart) is a medical problem.
Dieser Kaffee ist mir zu schwach, ich mag ihn stärker.
This coffee is too weak for me; I like it stronger.
To describe low intensity, 'schwach' (weak/faint) is often combined with sensory perceptions or signals: 'schwaches Licht' (weak/faint light), 'schwacher Wind' (weak/light wind), 'schwache Stimme' (weak/faint voice), or 'schwaches Signal' (weak signal).
Im Keller ist das Licht ziemlich schwach.
The light in the basement is pretty weak.
When it is about the quality of ideas or justifications, typical collocations are 'ein schwaches Argument' (a weak argument), 'ein schwacher Beweis' (weak evidence), or 'eine schwache Ausrede' (a weak excuse).
Für seine Verspätung hatte er nur eine schwache Ausrede.
He only had a weak excuse for being late.
strong
'stark' and 'schwach' are clear opposites. For people, 'stark' means that someone has a lot of strength, and 'schwach' means that someone has little strength or energy. For things like light, signals, performance, or arguments, 'stark' means that something is clear or convincing, and 'schwach' means that it has little effect. The context shows whether it is about physical strength, intensity, or quality.

Im Keller war das WLAN-Signal sehr schwach.
In the basement, the Wi-Fi signal was very weak.
Nele ist stark genug, um die schwere Kiste allein zu tragen.
Nele is strong enough to carry the heavy box by herself.