Scorpio n.

type of arachnid inhabiting warm regions, notable for its large "nippers" and the painful sting in its tail, c. 1200, scorpioun, perhaps late Old English, from Old French scorpion (12c.), from Latin scorpionem (nominative scorpio), extended form of scorpius, from Greek skorpios "a scorpion" (from PIE root *sker- (1) "to cut"). The Spanish alacran "scorpion" is from Arabic al-'aqrab. It was symbolic in Middle English of a treacherous person. As the zodiac sign by late 14c. Related: Scorpioid.

Centipeds and tarantulas are often confounded in the popular mind with scorpions, as are also various small lizards, in the latter case probably from the habit some of them have of carrying their tails up. Thus, in the United States, some harmless lizards or skinks, as of the genera Sceloporus and Eumeces, are commonly called scorpions. [Century Dictionary, 1895]