Wikipedia
A goedendag (also rendered godendac, godendard, godendart, and sometimes conflated with the related plançon) was a weapon originally used by the militias of Medieval Flanders in the 14th century, notably during the Franco-Flemish War. The goedendag was essentially a combination of a club with a spear. Its body was a wooden staff roughly five feet (150 cm) long with a diameter of roughly four inches (10 cm). It was wider at one end, and at this end a sharp metal spike was inserted by a tang.
The name "goedendag" derives from Dutch, usually taken in English sources to have meant "good day", with reference to the Bruges Matins massacre in 1302, at which the guildsmen of Bruges purportedly took over the city by greeting people in the streets, and murdering anyone who answered with a French accent. This derivation of the name may however be spurious. The Flemish themselves referred to the weapon as a "spiked staff" (gepinde staf). Another theory is that it's related to Germanic/English "dagger", so instead of "good day" it may have meant "good dagger". "Dag(ger)" isn't used anymore in current Dutch, while "goedendag" is still correct in current Dutch as "good day".
The weapon was used to great effect by the guildsmen of Flanders' wealthy cities against the French knights at the Battle of the Golden Spurs near Kortrijk (Courtrai) on 11 July 1302. The goedendag is frequently seen in the hands of Flemish militia in contemporary depictions of the battle, such as the carvings on the Courtrai Chest, a 14th-century wooden chest. It is also seen on a now-faded fresco from the Leugemeete in Ghent.