Lamia is a monster that lives mostly in the deserts. It is also the name of a weapon named after the creature, a spiky whip, forbidden in most countries.
In the PnP RPG
According to the Wiedźmin: Gra Wyobraźni RPG, Lamia is a creature thought by some to be related to vampires. Lamias are resistant to iron. Lamias are snakes with heads and bodies of beautiful women that can polymorph to a full-bodied woman to lure their victims into traps.
In The Witcher computer game
In one of the opening scenes of Act I, when Geralt first meets Shani in the compound surrounding the Inn, she tells him that the Salamandra had beaten a child with a lamia. This serves to underline the extent of their evil.