Definition of red adder in English:

red adder

noun

rare
  • 1US the copperhead snake, Agkistrodon contortrix; (also) a variety of the harmless milk snake, Lampropeltis triangulum, which somewhat resembles it.

  • 2British a small reddish variety of the adder, Vipera berus.

Origin

Early 19th century; earliest use found in American Journal of Science.