
English and German: metonymic occupational name for a glazier or glass blower from Old English glæs ‘glass’ Middle High German glas. In English the name may also derive from a nickname from Old French glas clas ‘clash of arms noise tumult (of battle)’. Irish (Ulster) Welsh Cornish and Scottish: from an Anglicized form of the epithet glas ‘slate colored gray’ or any of various Gaelic surnames derived from it. German: from an altered form of the personal name Klass a shortened form of Nikolaus (see Nicholas ). This surname is also found in France (Alsace and Lorraine). Jewish (Ashkenazic): artificial name from German Glass ‘glass’ or a metonymic occupational name for a glazier or glass blower (compare 1 above). Germanized or Americanized form of Slovenian Glas ‘voice’.
Source: Dictionary of American Family Names 2nd edition, 2022