Lam: An escape, especially from custody; an act of running or flight.
Headline and photo via Atlas Obscura, August 5, 2016.
On the lam is favored by journalists aiming for a combination of wry humor and tough-guy slang. For some reason, it’s especially popular in animal stories: I found news reports of goats, a cow, a steer, a capybara, and a lynx on the lam. (The lynx attacked four lambs while on the lam.) The recent found-panda story isn’t even the first collocation I found of on the lam and red panda: Masala the red panda escaped from a zoo in Eureka (California) in November 2015 and spent “a few tense days on the lam,” according to SFGate.com. It also shows up in stories about murder suspects, mob bosses, and a fugitive rabbi.
The phrase arose in the U.S. underworld; it first appeared in print (as “take it on a lam”) in a 1904 book, Life in Sing Sing, according to the Random House Historical Dictionary of American Slang. It entered widespread use in the 1920s and has been kept alive ever since by detective novelists and the aforementioned journalists. Its origin isn’t known for sure, but it may have developed from a verb lam, possibly of Scottish origin, that has meant “to beat” or “to strike” since the late 1500s. It would thus be related to lambaste (a blend of lam and baste, to thrash). If so, according to the Online Etymology Dictionary, “the word [lam] has the same etymological sense as the slang expression beat it.”