Cassidy suggests that mucker, a word used colloquially in Ireland and England to mean mate or friend, comes from the Irish mucaire, which is from muc meaning ‘pig’. According to Dineen the word mucaire means a swineherd, a boor, a rustic. Ó Dónaill’s dictionary only gives the meaning ‘a slovenly worker’. How you get from any of these meanings to the notion of a mate is beyond me.
Back in the real world, muck is a very old word in English (derived from Old Norse) which means dirt. A mucker is someone who works with this dirt (as in a mucker-out) but this is probably not directly the origin of mucker in the sense of friend. For this, we need to look at the way that people mucking about or messing about are often having fun together. That’s why we have muckers. So it is far more likely that the word mucker in all its senses is a reference to the English muck + er than that it has any connection with mucaire. As usual, Cassidy ignores the obvious English explanation in favour of a specious derivation from Irish.
Incidentally, while researching this post, I found that others say that mucker comes from the Irish mo chara, meaning my friend. This is also nonsense. As any competent Irish speaker will tell you, it’s a chara, not mo chara when you are talking directly (i.e. vocatively) to your friends. Of course, it is quite acceptable to talk about people in the third person using mo chara, but this would hardly give rise to a loanword, as the mo is not intrinsically linked to the word cara. Only the core form of the word, cara, would be borrowed in a bilingual situation. For example, we have all heard French-speaking characters in films saying things like ‘how are you, mon ami?’ This is a vocative use, like ‘a chara’. But when the Spanish word amigo is used in English, it is always used simply as amigo, never as mi amigo or su amigo, and so it is quite reasonable to assume that people might say things like ‘he is a great cara of mine’, but not *’it’s good to have a mo chara‘ (or do chara or ár gcara, for that matter). In any case, this claim was made by other idiots, not by Cassidy, so it is merely an aside and has no bearing on the substance of this blog.