nounThe American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
- A block used as a building material, especially a cinder block.
- A small wooden or plastic cube used as a building toy.
- A basic element or part of something: Amino acids are the building blocks of proteins.