or clinker brick plural clinker bricks: a brick that has been burned in the kiln to the point of becoming darkened or deformed
… the shiny, burnt, misshapen bricks, known as clinkers, which are the unloved and usually unused outer layer of the firing process. When banged together, they make a clinking sound. Stephen Best
… "clinkers," bricks that were discarded because they became deformed or discolored after getting too close to the heat in the kiln. Katy Tomasulo
"Over-baked and distorted," he [an unidentified Melbourne, Australia brick recycler] explained. Even so, these days retrieved clinker bricks can sell for over $1 each! Jenny Brown
Its corner-wrapping porch is complemented by generous eaves and abundant use of clinker brick—dense, misshapen bricks created by exposure to high temperatures … Sarah Hilbert
… a clinker-brick two-story orphanage … Anthony Doerr
2
: stony matter fused together
The manufacturing of cement involves the mixing of limestone, silica, iron oxide, and alumina. This mixture is heated by coal to very high temperatures … , transforming the mixture into a pebble-like substance called clinker, which is then mixed with gypsum and ground to a fine powder to make cement. Paul Robbins
also: a piece of clinker
When I was a kid in Parma, one of the chores assigned to me and my brothers was the removing of the "clinkers" from the old coal furnace in the basement of our house, as well as the one in the church next door. Loren Yadon