Do·rignis Cú ocus Cethen dím.

Do·rignis Cú ocus Cethen dím.

(you have made * Cú * and * Cethen * of me)

You have destroyed me completely.

This proverbial saying is found in a marginal note (an example of scribal graffitti) in the Book of Leinster (LL 161). The meaning can only be deduced from the scrap of narrative that accompanies it:

Doringnis Cú 7 Cethen dím .i. Cú thanic i tech Cormaic hú Chuind coro marb Cethen in rannairi for lár in taige 7 coro marbad in Cú fo chetóir.

"You have made Cú and Cethen of me. That is, it was Cú who came into the house of Cormac Ua Chuinn and killed Cethen the butler [the meat distributor] in the middle of the house, and the Cú was killed immediately."

Cú and Cethen are identified in Lebor Gabála Érenn as sons of Dian Cecht, the healer of the Túatha Dé. A verse there says that they both died "of terror in Aircheltra":

Atbath Cethen ocus Cú
do úathbás i n-Aircheltrú