1. building block - a single undivided natural thing occurring in the composition of something elsebuilding block - a single undivided natural thing occurring in the composition of something else; "units of nucleic acids"
unit
thing - a separate and self-contained entity
chemical chain, chain - (chemistry) a series of linked atoms (generally in an organic molecule)
couple - (physics) something joined by two equal and opposite forces that act along parallel lines
part, piece - 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
2. building block - a block of material used in construction work
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 Britain"
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