Old Norse was the inspiration for the some of the languages of Middle-earth. The Men of Lake-Town or Esgaroth spoke the in Language of Dale which was related to Rohirric and a dialect based on Old Norse between themselves, but Westron when talking to other people.
This was the language of the Vikings, though they would have probably called it Dansk Tongu (Danish Tongue). It is the language the old Icelandic sagas were written in, and Tolkien was quite familiar with it, having graduated with Old Norse as special subject. Modern Icelandic and Faroese are still fairly similar to Old Norse, though modern Scandinavian languages such as Norwegian, Danish and Swedish have diverged considerably from it.
Due to Danish invasions and settlement in parts of East and Northern England (the so-called Danelaw), many Old Norse words entered the English vocabulary: Law (lag), Knife (knífr), Cake (kake), Root (rót), Sale (sala), Stack (stakkr). Additional examples are listed at http://odin.bio.miami.edu/norse/words.html