Etymology: Scottish, supposedly from "ken no", as no male was supposed to be aware of its existence.
Perhaps a more common term is groaning cheese (a reference to the labors of the woman). Similar concepts are groaning malt (a strong ale provided for the women, or perhaps for the concerned father-to-be), groaning cake, and so forth depending on local tradition.
The cheese was made "for the refreshment of the gossips". In this early context, 'gossip' means a woman invited to attend the birth (originally, from 'god sibb', godparent or sponsor); its use in reference to idle talk came a little later.
Groaning cheese is mentioned as being provided by the husband (along with a cake), so this differs from kenno in that respect; kenno was prepared by the women of the family, and sliced and distributed to the women in attendance at the birth.
Many regional rituals and superstitions surrounded the groaning cheese: it was said to be eaten from the center outward to eventually form a large ring, through which the infant was passed on its christening day; and pieces of the cheese were tossed in "a certain nameless part of the midwife's apparel" (her smock) and given to young women, who were to place it under their pillow and dream of their lovers.
A Warwickshire Word Book says it is generally a sage cheese; Country Folk-lore says it is a Cheshire cheese, accompanied by a spiced rye loaf. The Encyclopedia of Superstitions refers to cake and new cheese. I'd be hungry if it weren't for that smock reference.