kahl
bald
Without hair on the head; having a bald head.
Er trägt eine Mütze, weil sein Kopf kahl ist.
He wears a hat because his head is bald.

bald / bare
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bald
Without hair on the head; having a bald head.
Er trägt eine Mütze, weil sein Kopf kahl ist.
He wears a hat because his head is bald.

The word 'kahl' (bald/bare) has a different meaning depending on the context. The noun it describes makes it clear whether it is about a head without hair, a tree without leaves, or an empty room.
Ein kahler Kopf braucht im Winter eine Mütze.
A bald head needs a hat in winter.
When talking about hair, 'kahl' (bald) is often used in the combinations 'ein kahler Kopf' (a bald head) or 'eine kahle Stelle' (a bald spot) on the head.
Viele Männer bekommen mit dem Alter eine kahle Stelle am Hinterkopf.
Many men get a bald spot on the back of their head as they age.
In nature, 'kahl' (bare) often describes trees, branches, or entire landscapes without vegetation. Typical combinations are 'kahle Bäume' (bare trees), 'kahle Äste' (bare branches), or 'ein kahler Felsen' (a bare rock).
Die Landschaft war nach dem Brand schwarz und kahl.
After the fire, the landscape was black and bare.
For rooms and surfaces, 'kahl' (bare) means unfurnished or undecorated. People often speak of 'kahle Wände' (bare walls), 'ein kahles Zimmer' (a bare room), or 'eine kahle Wohnung' (a bare apartment).
Ohne Bilder an den Wänden sieht das Zimmer sehr kahl aus.
Without pictures on the walls, the room looks very bare.
empty
'leer' and 'kahl' can both fit rooms or walls where there is little or nothing. 'leer' mainly says that there are no contents, no furniture, or no people there. 'kahl' additionally says that something looks bare, undecorated, or uncomfortable. For this reason, 'kahl' often sounds stronger and describes the impression more. Learners may confuse the words because a bare room can also be empty. If there is simply nothing inside, 'leer' is more natural; if it looks bleak and undecorated, 'kahl' fits better.

Ohne Bilder und Vorhänge wirkten die Wände sehr kahl.
Without pictures and curtains, the walls looked very bare.
Vor dem Umzug war das Wohnzimmer schon komplett leer.
Before the move, the living room was already completely empty.