thing - a separate and self-contained entity

chemical chain, chain - (chemistry) a series of linked atoms (generally in an organic molecule)

couple - something joined by two equal and opposite forces that act along parallel lines

piece, part - a portion of a natural object; "they analyzed the river into three parts"; "he needed a piece of granite"

unit cell - the smallest group of atoms or molecules whose repetition at regular intervals in three dimensions produces the lattices of a crystal

chemical group, radical, group - (chemistry) two or more atoms bound together as a single unit and forming part of a molecule

molecule - (physics and chemistry) the simplest structural unit of an element or compound

ashlar - a rectangular block of hewn stone used for building purposes

breeze block, cinder block, clinker block - a light concrete building block made with cinder aggregate; "cinder blocks are called breeze blocks in England"

headstone, keystone, key - the central building block at the top of an arch or vault

voussoir - wedge-shaped stone building block used in constructing an arch or vault

building material - material used for constructing buildings