an island of Denmark, 8 miles off the W. coast of Schleswig. Its area is about 15 square miles, and the soil is good, but the surface is so low that the continual efforts of the inhabitants are necessary to prevent it from being inundated by the sea. On the E. shore is the harbour of Ostersiel. Pelworm was formerly joined to the large island of Nordstrand, from which it was separated by a flood in 1684. Pop. 4000.