Skulduggery, which can also be spelled "skullduggery," was first documented in the mid-19th century spelled as "scull-duggery." Etymologists aren't sure exactly how the word arrived in English, but they do not believe it has anything to do with skulls. It is possibly derived from the now-very-rare "sculduddery," a term once used to refer to gross or lewd conduct, but unfortunately the origins of that word are also unknown.