Ooh! My Oxford Dictionary of British Place Names arrived in the mail yesterday. What serendipity!
Hebrides is from the Roman name for the islands, Ebudae or Ebudes. The meaning of the Latin name is unknown. The Old Scandinavian name is Suthreyar or southern islands, a relative designation being south Orkney and Shetland. The Gaelic is Innse Gail.
Rum is of unknown origin, probably pre-Celtic. The form Ruim dates to 677.
Eigg is Gaelic for indentation. The Gaelic name is Eilean Eigg, or island with an indentation. So it’s a reference to the island’s shape. The name appears in 1654.
Muc means pig in Gaelic and the name Helantmok, or island of pigs, dates to 1370.
The first element in Canna is of unknown origin. The second is from the Old Scandinavian ey, meaning island. The name Kannay appears in 1549.