the word even has its own wiki page
Tarbert (Scottish Gaelic: An Tairbeart) is a place name in Scotland and Ireland.
All placenames that variously show up as tarbert, tarbat or tarbet in their anglicised form derive from either the Irish or Scottish Gaelic an tairbeart, commonly translated as "the isthmus" today.
... This can be where two lochs nearly meet, or a causeway out to an island.
...Both these words derive from two Old Irish elements, 
tar "across" and
a nominalised form of the verb ber "to carry".
The /?/ in tar was assimilated to [/??/] -.
...So the literal translation would be an "across-carrying". The reason for this is that all tarberts are in fact located at or near old portage sites.
In English language spellings the first syllable "tar" has generally remained constant but the second syllable "bert" has variously been spelled as "bart", "bert" "bat", "bad" etc.

https://en.m.wikipedia.org/wiki/Tarbert#Examples