- unit, building block - a single undivided natural thing occurring in the composition of something else; "units of nucleic acids"
--1 is a kind of thing
--1 has parts: part, piece
--1 has particulars:chain, chemical chain; couple; unit cell; group, radical, chemical group; molecule - building block - a block of material used in construction work
--2 is a kind of building material
--2 has particulars:ashlar; cinder block, clinker block, breeze block; keystone, key, headstone; voussoir