Examining word fossils
The loss of inflections in Old English as it was on its way to becoming Middle English has left us with an interesting set of fossils using the plural ending -n.
This endures in one common word, oxen,
and one old-fashioned word, shoon
(as in, "The man in the moon had silver shoon").
But the remaining examples of the -n plural are all reduplicative. As Middle English simplified forms, sometimes two fading forms got mistakenly combined, and it stuck. The plural of child
but became children.
The plural of brother
and became brethren.
conceals the same process. Before we said "cow," we said "cu" for the beast. Middle English ku
had a plural, ky,
which attracted the ending -n because it looked like it needed something to become plural.
In modern Northumbrian dialect the word kye
remains. It is pronounced [kai]. With this lyric, you can see where English was heading before the southern dialect won out in the Middle Ages.
The kye's come hyem, but Aa see not me hinny,
the kye's come hyem, but Aa see not me bairn.
Aa'd rather loss all the kye than loss me hinny,
Aa'd rather loss all the kye than loss me bairn.