Building block (5)
'building block' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for brick that I've seen before include "Building unit?" , "Clay building block" , "Baked clay" , "Building material" , "Reliable person" .)
'building block' is the definition.
(synonyms)
This is all the clue.
(Other definitions for unit that I've seen before include "Separate part" , "Operational team" , "hospital department" , "One; military group" , "Self-contained section" .)