By Joe or By George

[clayaardvark]

What is the origin and meaning of the expressions "By Joe" and "By George"?

[Quizmonster]

I suspect you mean 'By Jove!' rather than 'By Joe!'. The god of the ancient Romans was originally named 'Jovis'. This was later compounded as 'Jovis-Pater' (Jovis the Father) and then - by telescoping these words together - as 'Juppiter/Jupiter'. Apart from being the joy-bringer, he was their supreme deity - the god of gods. To swear 'by' Jove, therefore, was to offer the mightiest of oaths and first appeared in English in the 16th century. There was also believed in those days to be a connection, because of the sound, with the name 'Jehovah'... God as presented in the Bible.

'By George!' is a similar type of oath dedicated to St George.