weak
The German word 'schwach' is used to describe something or someone that lacks strength or power. It can be used to describe physical weakness, such as a weak muscle or a weak immune system, or it can be used to describe emotional or mental weakness, such as a weak argument or a weak personality. The word can also be used as an adverb, as in 'schwach werden' which means 'to become weak'.
I feel weak today.
This sentence is using 'schwach' to express a physical state of not feeling strong. 'Ich fühle mich heute schwach' would be used to convey a temporary state of health or well being.
Your argument is weak.
In this context, 'schwach' is being used to express an opinion about the strength of an argument. Someone may say 'Dein Argument ist schwach' if they believe your argument lacks supporting evidence or is not persuasive.
The light is too weak to read.
Here, 'schwach' is applied to describe the intensity of light. 'Das Licht ist zu schwach zum Lesen' can be used when the light isn't strong enough to perform a particular task, such as reading.