masc. proper name, variant of Marcus (q.v.). Among the top 10 names given to boy babies born in the U.S. between 1955 and 1970.
Mark Twain is the pseudonym of American writer and humorist Samuel Langhorne Clemens (1835-1910), who had been a riverboat pilot; he took his pen name from the cry mark twain, the call indicating a depth of two fathoms, from mark (n.1) in a specialized sense of "measured notification (a piece of knotted cloth, etc.) on a lead-line indicating fathoms of depth" (1769) + twain.