I don't have too much information on this. I assume you know that caoineadh is the Irish (Gaelic) word for crying and in the context it means a lament. At Irish funerals in the past, some women used to sob loudly througout the wake. I gather that in some localities some of the women were so good at this they became almost professional and their services would be widely sought after.

Also, as far as I know, the word caoineadh is assocaiated with the wail or the howl of the bean si (banshee), the sound of which was said to be associated with, or sometimes to foretell a death.

Hope this was of some use, I'm sure there are people out there with a lot more auhoriative and detailed information on the subject.