Lacking an essential quality or element: deficient in common sense. (adjective)
Inadequate in amount or degree; insufficient: a deficient education. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "deficient" in a sentence
"Exactly how much vitamin D children and adults should get, and defining when they are deficient, is under debate."
"Because the thought that smokers are somehow mentally weak and that their lives are deficient is wrong."
"Unsupervised children wandering around with soulless eyes and vitamin deficient skin."