Old Blighty is a slang term for England.
According to many scholars, the word ‘blighty’ is actually from Hindi. The Hindi word that ‘blighty’ comes from is ‘vilayati’, meaning ‘foreigner’. In some dialects of Hindi, the word is pronounced ‘bilayati’. So ‘bilayati’ became ‘blighty’. The British soldiers in India began to use the word to refer to their own country. ‘Old Blighty’ was used as a term of endearment.
The term became popular only during the First World War. Homesick British soldiers sitting in the trenches in some foreign country began to refer to Britain as ‘dear Old Blighty’. Many poets and song writers writing during this period used this expression as well.
Soldiers coined the term ‘blighty wound’ as well. It was a serious wound, one that forced a soldier to leave the front line in order to recuperate. But it did not leave him a cripple. In other words, the wound was serious enough to get the soldier sent back home to England.
In other words, it was the sort of wound that could send the soldier back to Old Blighty. Sometimes, the soldiers inflicted the wound on themselves.