Tussu d'éc, missi d'anad...

Tussu d'éc, missi d'anad,
sírdursan ar sírscarad.

(you * to die * I * to remain
eternal sadness * our * eternal separation)

For you to die, for me to remain,
The everlasting sadness of our separation.

This is the second half of a stanza in which Cú Chulainn laments the death of his foster brother Fer Diad, who was manipulated into facing him in single combat by Medb and Ailill. This is the full stanza, from the LL Táin:

A Fir Diad, ardotchlóe brath,
dursan do dál dédenach,
tussu d'éc, missi d'anad,
sírdursan ar sírscarad.

Ciaran Carson's translation is:

Ah, Fer Diad, you were betrayed.
Our last meeting led to this,
my everlasting sorrow
that I live while you are dead.