Aiguille de Bionnassay, Alpine peak in Saint-Gervais-les-Bains, France

The Aiguille de Bionnassay is a high alpine summit on the border between France and Italy, sitting at 4,052 meters (13,294 ft) within the Mont Blanc massif. It forms a sharp peak covered in snow and ice, positioned at the western end of the ridge that leads toward Mont Blanc itself.

Florence Crauford Grove, Edward N. Buxton and Reginald S. McDonald, with guides Jean Pierre Cachat and Michel Payot, made the first ascent on 28 July 1865 by the north-west face, reaching the knife-edge summit ridge in a thunderstorm. The south ridge, now the normal route, was first climbed on 13 July 1888 by Kaspar Maurer, Andreas Jaun and Georg Gruber. The first winter ascent followed on 20 March 1929.

The name comes from a Celtic phrase meaning "where the goddess with the axe stands", from the Gaulish bio- (axe) and the suffix -sso. Climbers today follow the south ridge, the normal route opened in 1888, often after crossing the Dômes de Miage and a night at the Durier Hut.

The Durier Hut near Col de Miage on the French side is the usual starting point for the ascent. The exposed snow ridge near the top requires solid rope skills and experience on mixed terrain, so the peak is not suited for beginners.

The mountain's name comes from Continental Celtic: Bionnassay is analysed as "where the goddess with the axe stands", from a Gaulish word for axe or striker, a feminine divine suffix and a locational ending. The Celts depicted some deities holding an axe, as on the Pillar of the Boatmen in Paris.