An Etymological Dictionary of the German Language/Annotated/Sund
Sund, masculine, ‘sound, strait,’ early Modern High German only, a Middle German and Low German word; compare Anglo-Saxon sund, English sound, Old Icelandic sund, ‘sea, strait.’ The connection with Gothic sundrô, ‘separated’ (see sonders), is open to objection on account of the meaning (Sund, literally ‘division between countries and islands’?). It is preferable to link it with Anglo-Saxon and Old Icelandic sund, neuter, ‘swimming,’ which is an abstract of schwimmen (sunda- for swm-tó-, allied to the root swem); by this assumption Sund is regarded as ‘the place where one can swim.’