deficient

This word is most commonly used in formal or professional contexts, such as medical reports, legal documents, or technical evaluations. When describing a lack of something specific (like vitamins), it is often paired with the name of that substance (e.g., 'iron-deficient'). In general conversation, people often use simpler words like 'lacking' or 'not enough', but 'deficient' is used when you want to emphasize that a standard has not been met.