the GNU version of the Collaborative International Dictionary of English
adj. Having the qualities of a viper; malignant; venomous.
The Century Dictionary and Cyclopedia
Having the qualities of a viper; viperish; venomous; malignant; spiteful: chiefly said of mental qualities, or used figuratively.
Word Usage
"Expect a resolution in tonight's 90-minute finale, and while Jax is unlikely to end up dead (the series has been renewed), the viperous ATF rogue (Ally Walker) does hold the whip hand."