From Scots 'sculduddery' (adultery, obscenity), reshaped in 19th-century America to 'skulduggery' by folk etymology linking it to 'skull'. The meaning shifted from sexual misconduct to general underhanded trickery during the transatlantic crossing — a word transformed by immigration.
Underhanded or unscrupulous behaviour; trickery, dishonest scheming.
Almost certainly an American alteration of Scots 'sculduddery' or 'sculdudrie', which originally meant 'adultery, sexual impropriety, obscenity' in Scots from at least the 18th century. The Scots word may derive from an unrecorded Old English or Middle English compound, possibly related to 'sculdor' ('shoulder' — hinting at something done behind one's back?) or simply an expressive formation. The word crossed the Atlantic with Scottish immigrants and first appeared in American English in the 1850s–60s with the spelling 'skull-duggery', likely influenced by folk etymology connecting it to 'skull' (implying bone-deep trickery or death's-head deception). The shift from sexual impropriety to
Skulduggery is a rare case of a word being completely transformed by folk etymology during immigration. The original Scots 'sculduddery' meant sexual misconduct — Robert Burns's contemporaries used it for bawdy behaviour. When Scottish settlers brought it to America, someone heard 'skull' in the first syllable and respelled it accordingly, and the meaning shifted from bedroom scandal to political corruption. The earliest known American use (1856) is in a congressman's speech about electoral fraud. The skull had nothing