Especially U.S.: transferred use of the surname, originally a local name from any of the several places in England (for example, in Lancs., Staffs., Sussex, and W. Yorks.) named with Old English clǣg ‘clay’ + tūn ‘enclosure, settlement’.
English, German, Danish, and Swedish: nickname or byname for someone of a frosty or gloomy temperament, from Middle English, Middle High German, Danish, Swedish winter (Old English winter, Old High German wintar, Old Norse vetr). The Swedish name can be ornamental.