Isat craebsa nar craithead fa cnomheas.

Isat craebsa nar craithead fa cnomheas.

(you are * branch * that not * was shaken * for its * nut-mast)

You are a branch that has not been shaken for its nut crop.

When Congal says this to Maelduin in "Cath Muighe Rath" (FDG, p. 294), he means that Maelduin is an untested warrior, unhardened by battle.