Lamsters as a class are probably as old as the law from which they flee, but the term "lamster" didn't sneak into our language until the early 1900s, less than ten years after the appearance of the noun lam, meaning "sudden or hurried flight especially from the law" (as in the phrase "on the lam"). Both words have an old verb relation, though. "Lam" has meant "to beat soundly" or "to strike or thrash" since the late 16th century, but in the late 19th and early 20th centuries it developed another meaning: "to flee hastily." The origins of the verb are obscure, but etymologists suggest that it is Scandinavian in origin and akin to the Old Norse lemja, meaning "to thrash."