G3789 ὄφις (óphis)

KJV renderings: serpent
Strong's definition: a snake, figuratively, (as a type of sly cunning) an artful malicious person, especially Satan
Derivation: probably from G3700 (ὀπτάνομαι) (through the idea of sharpness of vision);

From James Strong's public-domain dictionaries (G), JSON edition by OpenScriptures (CC-BY-SA). Every dotted-underline word in the text links here.