deficient

Carries a clinical or technical tone. It suggests an objective gap between what is present and what is required for optimal function or legality. When applied to health (e.g., vitamins), it describes a biological shortfall. When applied to systems or performance, it implies a failure to meet a benchmark, often carrying a negative judgment of incompetence or negligence. Unlike "lacking," which can be neutral or descriptive, "deficient" often implies that the absence is problematic or harmful. It is more formal than "not enough" and more precise than "poor."