lautlos
silent
Describes something that happens or moves completely without any noise. Synonymous with quiet or noiseless.
Die Katze schlich lautlos durch den Garten.
The cat crept silently through the garden.

silent
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silent
Describes something that happens or moves completely without any noise. Synonymous with quiet or noiseless.
Die Katze schlich lautlos durch den Garten.
The cat crept silently through the garden.

The word is made up of 'Laut' (sound/noise) and the ending '-los' (-less), which means 'without'. So 'lautlos' literally means 'without sound' or 'without noise'.
Das Elektroauto fuhr fast lautlos an uns vorbei.
The electric car drove past us almost silently.
'Lautlos' is very often used as an adverb to describe a verb. In this form, the word stays unchanged and is not declined.
Der Dieb bewegte sich lautlos durch das dunkle Haus.
The thief moved silently through the dark house.
'Lautlos' is often combined with verbs of movement, for example 'schleichen' (to creep), 'gleiten' (to glide), 'sich nähern' (to approach), or 'sich bewegen' (to move).
Ein U-Boot kann sich lautlos unter Wasser bewegen.
A submarine can move silently underwater.
loud / according to
'laut' and 'lautlos' both describe how strongly something can be heard. But they are opposites. 'laut' means that a sound is strong and clearly audible. 'lautlos' means that something makes no sound at all or can hardly be heard. So the difference is not just 'quiet', but really 'without any noise'. 'laut' fits things like music, voices, or machines. 'lautlos' is more likely to fit movements or actions that happen silently.

In der Bibliothek schließt sie die Tür lautlos.
In the library, she closes the door silently.
Die Musik aus der Wohnung nebenan ist heute sehr laut.
The music from the apartment next door is very loud today.