adjective
1. lacking some essential part, element, substance, or characteristic.
Their diet is deficient in vitamin C.
She finds her daughter-in-law deficient in good manners.
The struggling nation is rich in natural resources but deficient in infrastructure.
With respect to piano skill, I’m sadly deficient.
2. inadequate in amount or extent.
His knowledge of mathematics is deficient, so he’s having difficulty with his physics course.