# deficient

/dɪˈfɪʃənt/ (US) · /dɪfˈɪʃənt/ (UK) · CEFR C1 · Adjective

Source: https://englishreference.com/word/deficient
Updated: 2026-05-06

## Definition

not having enough of something that is necessary, like a vitamin or a specific skill.

For teachers: lacking in a necessary quality, element, or amount. Often used in medical or technical contexts to describe a shortage that prevents proper functioning.

## Examples

- His diet is deficient in vitamin C.
- The inspection found that the building's fire safety measures were deficient and required immediate upgrades.
- While the theory was elegant in its simplicity, it proved deficient when applied to real-world data that accounted for environmental variables the researchers had initially ignored.

## Pitfalls

- Not "The report was deficient of details." but "The report was deficient in details." — The adjective 'deficient' collocations with 'in' rather than 'of' when specifying what is lacking.

## Usage notes

- Commonly followed by the preposition 'in'.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.