Proper noun
Oak Apple Day
(historical) An English public holiday, formerly observed on 29 May but abolished in 1859, commemorating the restoration of the English monarchy in 1660. People wore oak apples or sprigs of oak leaves, in reference to Charles II escaping the Roundhead army by hiding in an oak tree after the Battle of Worcester.
Synonyms: Oak and Nettle Day, Restoration Day, Royal Oak Day, Shick Shack Day, Shig Shag Day
The Royal Oak symbol and Oak Apple Day commemorate the escape of King Charles II from the grasp of the parliamentarians after his father's execution: he hid in an oak tree to avoid detection before safely reaching exile. Source: Internet