Sentence:  “Nay, daughter, when thou art as old as Notte it will be time enough to reckon years!” returned the dark-skinned sybil, <WSD>lithening</WSD> the stiff folds of a viper in a blue oil, which cast out a noisome perfume as she stirred it. 
Meaning of the word marked with <WSD> tags:  To make lithe, soften; to ease, mitigate