deficient

Compared meaning: not enough or not able (adjective).

比较义项：不够、不能胜任或缺乏必要的东西（形容词）。

• inadequate

  Describes a thing, amount or situation that fails to meet a particular need or standard, not a person's ability; typically followed by 'for'.

  描述事物或数量未能满足某种特定需要或标准，而非评价人的能力；常与介词 for 连用。

  The old bridge was inadequate for modern truck traffic.

  这座旧桥已不能满足现代卡车通行的需要。

• incapable

  Focuses on a person's inability to perform an action, often due to circumstance or lack of capacity, without necessarily judging skill; used with 'of' plus a verb-ing form.

  侧重人无法完成某个动作，往往是因为处境或能力所限，并不一定评价其技能；常与 of doing 连用。

  After the injury, he was incapable of lifting even light weights.

  受伤后，他连轻的东西都举不起来。

• incompetent

  Negatively judges a person's skill or professional ability, implying repeated failure to perform a job properly; stronger and more critical in tone than incapable.

  负面评价一个人的技能或职业能力，暗示其屡屡不能把工作做好；语气比 incapable 更强烈，更带批评意味。

  The incompetent electrician left wires exposed and dangerous.

  那个不称职的电工把电线裸露在外，十分危险。

• deficient 本词

  Describes something lacking a specific necessary component, quality or amount within it, typically followed by 'in'; neutral, technical register common in nutrition or systems.

  描述某事物缺少某种必需的成分、品质或数量，常与介词 in 连用；语气中性，常用于营养、系统等技术性语境。

  The soil was deficient in nitrogen, so the plants grew slowly.

  这片土壤缺氮，所以植物长得很慢。

Inadequate, incapable, incompetent and deficient mean not enough or not able. Inadequate describes a thing that fails to meet a need. Incapable means a person cannot do something, without judging skill. Incompetent judges a person's poor job skill. Deficient means lacking a necessary part.

这四个词都可表示不够或不能，但适用对象和语气不同：inadequate 侧重事物或数量不足以满足某种需要；incapable 侧重人（或事物）因能力或处境所限而做不到某事，语气较中性；incompetent 专指人缺乏做好某工作所需的技能，带有批评意味；deficient 侧重缺少某种必需的成分或素质，语气中性、技术性强。这里不比较 inadequate 表示自卑、觉得能力不够好的用法，也不比较 incompetent 在法律或医学语境中表示不具备资格的用法。

Compared meaning: not enough for a need (adjective).

比较义项：不充分的（形容词）。

• inadequate

  A general word for not enough or not good enough for a particular purpose; used broadly for equipment, preparation, funding, etc.; typically followed by 'for'.

  泛指数量或质量不足，无法满足某种特定需要；可广泛用于设备、准备工作、资金等；通常后接“for”。

  The lighting in the office was inadequate for reading small print.

  办公室的照明不足，无法看清小字。

• deficient 本词

  Points to a lack of a specific necessary element or quality, typically followed by 'in'; common in nutrition, health and technical contexts; sounds more formal or clinical.

  强调缺少某种具体的必需成分或要素，通常后接“in”；多见于营养、健康和技术等正式语境，语气更显专业、生硬。

  His diet was deficient in vitamins, so he felt tired.

  他的饮食缺乏维生素，所以他感到疲惫。

Inadequate and deficient both mean not enough. Inadequate is general, meaning not enough or not good enough for a purpose, often followed by for. Deficient points to a lack of one specific necessary part, often followed by in, and sounds more formal or clinical.

这两个词都表示“不够、不充分”，但inadequate泛指数量或质量不足以满足某种需要，用法宽泛，常搭配“for”；deficient则强调缺少某种具体的必需成分或要素，常搭配“in”，多见于营养、健康、技术等较正式的语境。这里只比较“不充分”这一义项，不涉及两词的其他用法。