Viper - Vine's Expository Dictionary of New Testament Words
Viper
[ 1,,G2191, echidna ]is probably a generic term for poisonous snakes." It is rendered "viper" in the NT,
(a) of the actual creature, Acts 28:3;
(b) metaphorically in Matthew 3:7; Matthew 12:34; Matthew 23:33; Luke 3:7.