The word madadh (madra being an extension formed with a collective suffix -ra) seems to have originally meant a cur or common dog (perhaps, ironically, more like пёс in Russian, if the usage notes in the Wiktionary entry are to be believed); cú (cognate with Latin canis and English hound) was reserved for somewhat nobler specimens, and nowadays, yes, you'd probably encounter it more in literature than in real life.
Similarly with horses, capall originally referred to a draught horse and each to a saddle horse or a chariot horse. In both cases social changes probably favoured the spread of one word at the expense of the other. In a further development, Ulster Irish speakers nowadays use the word capall to mean "mare" (láir in Standard Irish), and the general word for the animal there is beathach, a word whose basic meaning is "beast, animal". (Incidentally, the Latin word caballus = "horse", from which Spanish caballo, French cheval, Italian cavallo, etc., and ultimately English cavalry, cavalier, chivalry, etc. all derive is originally a Celtic word, borrowed by the Romans from Gaulish, a sister language of Irish).
Thank you, very interesting! I had been wondering about the difference for quite some time but surmised (erroneously) that "cú" is just more archaic and used mostly in myths or more figuratively (assumption made because of Cú Chulainn I guess).
In Russian "cú" is usually translated as "пёс" (means "dog" but refers only to male dogs), and there's also a more generic term, "собака" (a feminine noun; the word was borrowed from Middle Iranian long time ago) which refers to any kind of dogs.
@Coligno, you're a treasure trove of valuable information, that's for sure! And I guess I just should've been more attentive at school during history lessons but I had no idea the whole concept of trousers was alien to the Romans before the Gauls. I wanted to say something about the wonderful Mediterranean climate but, coming to think of it... kilt, for example... maybe it isn't about climate after all.
@K P, haha, maybe you're right about applying the term to other animals. I remember my school classmate's grandfather saying "любит печенье, собака" about their cat that used to steal cookies from the table — in such a gentle manner that it sounded almost like a term of endearment. But I don't think I've ever heard it anywhere else, and I, too, think that the derogative uses of these two words (собака and пёс) aren't really common nowadays.
Kseniia, you say you surmised erroneously, but I believe correctly: "cú" IS the more archaic and literary form, as well as still used in Scotch Gaelic.
The word for "horse" is somewhat similar, the more common current word in Ireland being "capall" (cognate with Spanish "caballo"), but the more archaic and literary word being "each" (cognate with Latin "equus"), still seen in placenames and expressions, and I believe in everyday modern Scotch Gaelic.
I guess dogs and horses had always been the most important animals, right?
