A groin vault or groined vault (also sometimes known as a double barrel vault or cross vault) is produced by the intersection at right angles of two barrel vaults. The word groin refers to the edge between the intersecting vaults; cf. ribbed vault. Sometimes the arches of groin vaults are pointed instead of round. In comparison with a barrel vault, a groin vault provides good economies of material and labour. The thrust is concentrated along the groins or arrises (the four diagonal edges formed along the points where the barrel vaults intersect), so the vault need only be abutted at its four corners. See Wikipedia.
In South Africa the device can be found in the Norman Revival Churches of Herbert BAKER as well as in his design for the loggia for Rhodes University in Grahamstown and the Union Buildings in Pretoria, the Romanesque Revival Churches of Gerard MOERDYK, for example Pretoria East NGK, as well as earlier in the mannered neo-classicism of Louis THIBAULT, for example the original entrance to the Old Supreme Court in Cape Town.