Another ridiculous claim of Cassidy’s which has been spread far and wide by an uncritical readership on the internet is the idea that the Plug Uglies, a 19th century criminal gang, derive their name from Baill Óglaigh, which he claims means “a member of the Volunteers.” He says that this refers to the Fenian Brotherhood.
There are several problems with this. Firstly there are a number of explanations for the phrase in English. Check out these explanations here: http://www.worldwidewords.org/nl/ynmb.htm
Secondly, as usual, Cassidy’s version is rubbish. His knowledge of Irish (I use the term ‘knowledge’ advisedly) lets him down. Baill would require the partitive dative preposition de, so it would be Baill de na hÓglaigh (members of the Volunteers), not baill Óglaigh (a Volunteer’s members!!). Thus, ‘one of the men’ is duine de na fir, not duine na bhfear, which if it means anything, means ‘the person belonging to the men, the men’s personal slave.’
And then again, Cassidy failed to understand the way language works. He was obviously not a very intelligent man and thought you could simply lift words from the dictionary and do what you like with them, regardless of their history or usage. Óglach doesn’t really mean a volunteer. What it means is a young warrior or a soldier. It is an old word in the language but it was used for the first time as a translation for the Irish Volunteers in the years just before the First World War, when the Irish Republican Army was translated as Óglaigh na hÉireann. To the best of my knowledge, it was never used as a word for the Irish Republican Brotherhood or Fenian Brotherhood several generations before that, so the idea that it is a reference to this is absurd.
Also, you have to take into account that none of these phrases really sound a lot like Plug Uglies anyway (bwill ohglee, bwill de na hohglee).
Chance of Cassidy being correct – 0%!