blast celln.1. A precursor of a human blood cell.2. An immature, undifferentiated cell.[-blast + cell.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.blast? cell` n. Biol. any undifferentiated or immature cell. [1950?55;