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στυγνόν

From LSJ

Sunt verba voces quibus hunc lenire dolorem possis, magnam morbi deponere partem → Words will avail the wretched mind to ease and much abate the dismal black disease.

Horace, Epistles 1.34

Russian (Dvoretsky)

στυγνόν:
I τό угрюмость, суровость Xen.
II adv. ужасно, страшно: σ. οἰμώξας Soph. закричав страшным голосом.