"Thom" is one of the main Sept Names of Clan
MacThomas.
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Thom is perhaps
the most common of all the family names or surnames adopted by
members of Clan MacThomas as they migrated across Scotland and
the world. "Tam" is thought to be a variant of spelling of
Thom. It is thought likely that there are actually a number of
different Thom septs as families in different areas took the
same name.
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The migration
map on this website shows the Thom
name in South West Scotland, North East Scotland and in the
Dundee area.
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By the
twentieth century there were groupings of Thom's in Eastern
and North Eastern Scotland, South West Scotland, Glasgow and
Edinburgh. Additionally there were many thousands with the
name living in England, Australia, New Zealand and North
America.
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There is much
more about all the Clan's septs in the book
"The History of
the Clan MacThomas" compiled by Andrew MacThomas of
Finegand.