lam (n.) Look up lam at
"flight, escape," as in on the lam, 1928, in pickpocket slang, (according to OED attested from 1897 in do a lam), from a U.S. slang verb meaning "to run off" (1886), of uncertain origin, but perhaps from lam (v.), which was used in British student slang for "to beat" since 1590s (compare lambaste); if so, the word has the same etymological sense as the slang expression beat it.
lam (v.) Look up lam at
also lamm, "to thrash, beat," 1590s, a slang, provincial or colloquial word, probably from Old Norse lemja "to beat," literally "to lame," which is cognate with the native verb lame (see lame (adj.)). Related: Lammed; lamming.