1. lacking in some necessary quality or element; inadequate or insufficient
2. having a deficiency; below normal or required standards
Usage: often used in medical or nutritional contexts

Examples

• The soil in this area is deficient in essential nutrients.
• Her diet was deficient in vitamin D.
• The report was deficient in supporting evidence.
• Students who are deficient in basic math skills need extra help.
• The building’s security system was found to be deficient.
• His immune system became deficient after the illness.