1 Class of masonry consisting of blocks of accurately dressed, cut, squared, and finished stone (the Roman opus quadratum), faced and with clean sharp arrises, forming perfect courses, laid in mortar. It is contrasted with rubble. Thin slabs of similar masonry, used as a facing to a brick wall or as paving slabs, were also termed ashlar, although bastard ashlar is preferred. Finished work featuring the faces of each stone projecting beyond the line of the joints is rustication, or rusticated ashlar, and can be of several types.
2 Large clay-based block larger than a brick, such as faïence or terracotta (US).