haff (n.)

also haaf, Baltic lagoon, separated from open sea by a sandbar, German, from Middle Low German haf "sea," from Proto-Germanic *hafan (source also of Old Norse haf, Swedish haf "the sea," especially "the high sea," Danish hav, Old Frisian hef, Old English hæf "sea"), perhaps literally "the rising one," and related to the root of heave, or a substratum word from the pre-Indo-European inhabitants of the coastal regions. The same word as haaf "the deep sea," which survived in the fishing communities of the Shetland and Orkney islands.