οὐ δικαίως θάνατον ἔχθουσιν βροτοί, ὅσπερ μέγιστον ῥῦμα τῶν πολλῶν κακῶν → unjustly men hate death, which is the greatest defence against their many ills | men are not right in hating death, which is the greatest succour from our many ills
from the base of κῦμα (through the idea of circularity; compare κύκλῳ, εἱλίσσω); to roll about: wallow.
