The story
- Scots · borrowed fromsculduddery
- English todayskulduggery
An alteration of Scots sculduddery, sculdudrie (“adultery, unchaste behaviour; obscenity, lewdness”), of long-uncertain origin (probably a euphemism). Relation to skull is speculative at best and likely folk etymology. The American spelling skullduggery is in keeping with terms such as skillful and willful.
Etymology from Wiktionary, CC BY-SA 4.0.