Galion

Tolkien does not explain the name Galion, but he does note (in comments reproduced in The History of the Hobbit) that it is 'not Sindarin (though perhaps 'Sindarized' in shape)'. This presumably means that Galion's original name - if it had a meaning at all - was derived from Silvan Elvish, adapted to the native speech of his master, the Sindarin Elvenking Thranduil. This makes speculation on the name's meaning extremely difficult, though certain elements are at least suggestive.

The -ion ending in Elvish names typically indicates a patronymic, so Galion's name seems to show that he was the son of an Elf with a name like 'Gal', or at least incorporating that element. Gal- in Elvish names usually means 'green', so the extended meaning of the name Galion is probably something like 'son of the green Elf'.

Gal- can also be read as 'light', so potentially Galion would be 'son of light', but given that his Forest home was known in Elvish as Eryn Galen ('Greenwood') the connection with 'green' seems more plausible.

Historically, the word 'butler' originally referred to a cup-bearer, or servant responsible for managing and serving wine (the word comes from Old French boteillier, literally 'bottler'). The fact that Galion was in charge of serving wine to the Elvenking implies that, at least to some extent, Tolkien had this older meaning of the word in mind when he described Galion as the king's butler.