lässig
casual
A relaxed, informal, and uncomplicated manner or appearance.
Er trug ein lässiges Hemd und eine verwaschene Jeans.
He wore a casual shirt and faded jeans.

casual
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casual
A relaxed, informal, and uncomplicated manner or appearance.
Er trug ein lässiges Hemd und eine verwaschene Jeans.
He wore a casual shirt and faded jeans.

The adjective 'lässig' (casual) is related to the verb 'lassen' (to let/leave). The basic idea is that you 'leave' things as they are, meaning you are carefree and relaxed.
Er hat eine sehr lässige Art, mit Problemen umzugehen.
He has a very casual way of dealing with problems.
'Lässig' (casual) can be positive (relaxed, cool) or negative (careless, indifferent). The context makes the difference: if it is about style or effortlessness, it is positive. If it is about duties or rules, it is often meant negatively.
Sie hat einen sehr lässigen und eleganten Kleidungsstil.
She has a very casual and elegant style of dress.
In the meaning of 'zwanglos' (informal/casual), 'lässig' (casual) often describes clothing or personal style. Typical combinations are 'lässige Kleidung' (casual clothing), 'ein lässiger Look' (a casual look), or 'lässig gekleidet sein' (to be dressed casually).
Für die Party am Strand ist ein lässiges Outfit perfekt.
A casual outfit is perfect for the party on the beach.
To express effortlessness, 'lässig' (casually/effortlessly) is very often used as an adverb. It then describes how an action is carried out: with apparent ease.
Er lehnte lässig an der Wand und beobachtete die Szene.
He leaned casually against the wall and watched the scene.
The negative meaning 'nachlässig' (careless) is often found in the fixed expression 'ein lässiger Umgang mit etwas' (a careless approach to something). It criticizes someone for not taking an important matter seriously enough.
Die Firma wurde für ihren lässigen Umgang mit Kundendaten kritisiert.
The company was criticized for its careless handling of customer data.
cool
'cool' and 'lässig' often describe something positive, relaxed, or modern. 'cool' is very colloquial and can simply mean 'great', 'impressive', or 'calm in a stressful situation'. 'lässig' puts more emphasis on a relaxed, informal manner, or on someone doing something without much effort. Learners may confuse the words because both can fit clothing, behavior, or people. If you want to say that something is very good or impressive, 'cool' is more natural. If the relaxed manner is the main focus, 'lässig' fits better.

Beim Vortrag stand sie ganz lässig vor der Gruppe.
During the presentation, she stood very casually in front of the group.
Das neue Fahrrad von Max sieht richtig cool aus.
Max's new bike looks really cool.