Millfet lí th'aigthe!

Millfet lí th'aigthe!

(I will destroy * beauty * of your face)

I will destroy the beauty of your face. = I will kill you!

The threat is found in the Metrical Dindsenchas in the 25th stanza of the poem "Ceilbe". The word "lí" can mean "splendor, beauty, luster, beautiful complexion, color".