Tavish information can be found here
http://www.mactamhais.liquidweb.com/history.htmThe name Tavish comes from the Clan MacTavish
What I don't know is if Taus or Tavis is actually a form of
Thomas or if it was a Gaelic name that was anglicised to
Thomas. Taus was the founder of the MacTamhais Clan which phonetically is spelled MacTavish. The name Taus (Tavis) dates back atleast to 1100 AD, which is when the Clan was founded. I know many gaelic names where just anglicised to biblical names- like
Tadhg to
Timothy even though the names are completely unrelated.