1: ἔχιδνα
(Strong's #2191 — Noun Feminine — echidna — ekh'-id-nah )

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; 12:34; 23:33; Luke 3:7 .