Five straits are named 'belt' (Danish: bælt), the only ones in the world[clarification needed]. Several other straits are named 'sound' (Danish, Swedish and German: sund). Where an island is situated between a "belt" and a "sound", typically the broader strait is called "belt" and the narrower one is the "sound":
Sound/Sund: Aldersund separating Aldra island (left) from mainland Norway.
The Germanic word "sound" has the same root as the verb to sunder in the meaning of "to separate". The Old Norse form of that verb is sundr. In Norway hundreds of narrow straits separating islands and combining fjords or outer parts of fjords are named "Sund".
Another explanation derives "sound" from an ancient verb "sund" in the meaning of to swim. That way a sound is a swimmable strait. In the Swedish language any strait is called "sund".
The Germanic word "sound" is not related to the Romance languages originated word "sound", which has developed from the Latinsonus.[citation needed]