-tasun

From earlier -tarzun (still in use in the north), from -tar (“ethnonymic suffix”) +‎ -zun (“suffix of unknown meaning also present in -kizun, of the same meaning”).

• IPA^(key): /tas̺un/, [t̪a.s̺ũn]

-tasun

1. Forms nouns from adjectives, -ness, -th

   ‎eder (“beautiful”) + ‎-tasun → ‎edertasun (“beauty”)

   ‎luze (“long”) + ‎-tasun → ‎luzetasun (“length”)

• “-tasun”, in Euskaltzaindiaren Hiztegia [Dictionary of the Basque Academy] (in Basque), Euskaltzaindia [Royal Academy of the Basque Language]
• “-tasun”, in Orotariko Euskal Hiztegia [General Basque Dictionary], Euskaltzaindia, 1987–2005