Some Lithuanian sources state that Matas is a short form of Motiejus. I suppose that means that that is how it originally was and that back then, Motiejus was the main Lithuanian form of Matthew. However, since then, Matas has turned into an independent name, even though there should still be plenty of instances today where it is used as a short form of Motiejus (and also its variant spelling Matiejus as well as the numerous variant forms, such as Matėjas, Matėjus and Motėjus). As a result, Matas is now the most popular form of Matthew in Lithuania today, with Motiejus being in second place.- https://de.wikipedia.org/wiki/Matas_(Vorname) (in German) - https://www.tevu-darzelis.lt/vaiku-vardai/Matas/ (in Lithuanian; mentions that Matas is an abbreviation ("trumpinys") of Motiejus and Matiejus) - http://www.vardai.org/vardo-reiksme/Matas/ (in Lithuanian) - http://day.lt/vardai/Matas (in Lithuanian) - http://vardai.vlkk.lt/vardas/Matas (in Lithuanian; mentions that Matas is a 'trumpinys', which means "abbreviation" in English).
- https://de.wikipedia.org/wiki/Matas_(Vorname) (in German)
- https://www.tevu-darzelis.lt/vaiku-vardai/Matas/ (in Lithuanian; mentions that Matas is an abbreviation ("trumpinys") of Motiejus and Matiejus)
- http://www.vardai.org/vardo-reiksme/Matas/ (in Lithuanian)
- http://day.lt/vardai/Matas (in Lithuanian)
- http://vardai.vlkk.lt/vardas/Matas (in Lithuanian; mentions that Matas is a 'trumpinys', which means "abbreviation" in English).